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The Crusades were a series of religious wars sanctioned by the Latin Church in the medieval period. The most commonly known Crusades are the campaigns in the eastern Mediterranean aimed at recovering the Holy Land from Muslim rule, but the term crusade is also applied to other church-sanctioned campaigns. These were fought for a variety of reasons including the suppression of paganism and heresy, the resolution of conflict among rival Roman Catholic groups, or for political and territorial advantage. At the time of the early Crusades the word did not exist, only becoming the leading descriptive term around 1760.
In 1095, Pope Urban II called for the First Crusade in a sermon at the Council of Clermont. He encouraged military support for the Byzantine Empire and its Emperor, Alexios I, who needed reinforcements for his conflict with westward migrating Turks colonising Anatolia. One of Urban's aims was to guarantee pilgrims access to the eastern Mediterranean holy sites that were under Muslim control. Although scholars disagree over whether this was the primary motive for Urban, or for those who heeded his call. Urban's strategy may have been to unite the eastern and western branches of Christendom, which had been divided since the East–West Schism of 1054, and to establish himself as head of the unified Church. The initial success of the Crusade established the first four Crusader states in the eastern Mediterranean: the County of Edessa, the Principality of Antioch, the Kingdom of Jerusalem and the County of Tripoli. The enthusiastic response to Urban's preaching across all social strata in western Europe established a precedent for other Crusades. Volunteers became Crusaders by taking a public vow and receiving plenary indulgences from the Church. Some were hoping for a mass ascension into heaven at Jerusalem or God's forgiveness for all their sins. Others participated to satisfy feudal obligations, obtain glory and honour or to seek economic and political gain.
The two-century attempt to recover the Holy Land ended in failure. Following the First Crusade there were six major Crusades and numerous less significant ones. After the last Catholic outposts fell in 1291, there were no more Crusades to recover the Holy Land; but the territorial gains lasted longer in northern and western Europe. Crusades brought all the north-east Baltic and the tribes of Mecklenburg and Lusatia under Catholic control in the late 12th century. The Teutonic Order created a Crusader state in Prussia in the early 13th century and the French monarchy used the Albigensian Crusade to extend the kingdom to the Mediterranean Sea. The rise of the Ottoman Empire in the late 14th century prompted a Catholic response which led to further defeats at Nicopolis in 1396 and Varna in 1444. Catholic Europe was in chaos and the final pivot of Christian–Islamic relations was marked by two seismic events: the fall of Constantinople to the Ottomans in 1453 and a final conclusive victory for the Spanish over the Moors with the conquest of Granada in 1492. The idea of Crusading continued, not least in the form of the Knights Hospitaller, until the end of the 18th-century but the focus of western European interest moved to the New World.
Modern historians hold widely varying opinions of the Crusaders. To some, their conduct was incongruous with the stated aims and implied moral authority of the papacy, as evidenced by the fact that on occasion the Pope excommunicated Crusaders. Crusaders often pillaged as they travelled, and their leaders generally retained control of captured territory instead of returning it to the Byzantines. Intolerance of other faiths and traditions was increased with Jews, those considered heretics and Muslims murdered in their thousands on several occasions. One of which was the sack of christian Constantinople during the Fourth Crusade. However, the Crusades had a profound impact on western civilisation: Italian city-states established colonies which permitted trade with the eastern markets even in the Ottoman period, allowing Genoa and Venice to flourish; the collective identity of the Latin Church was consolidated under papal leadership; and they constituted a wellspring for accounts of heroism, chivalry, and piety that galvanised medieval romance, philosophy, and literature. The Crusades also reinforced a connection between western Christendom, feudalism, and militarism.
The term crusade used in modern historiography at first referred to the wars in the Holy Land beginning in 1095, but the range of events to which the term has been applied has been greatly extended, so that its use can create a misleading impression of coherence, particularly regarding the early Crusades. The term used for the campaign of the First Crusade was iter "journey" or peregrinatio "pilgrimage". The terminology of crusading remained largely indistinguishable from that of pilgrimage during the 12th century, reflecting the reality of the first century of crusading where not all armed pilgrims fought, and not all who fought had taken the cross. It was not until the late 12th to early 13th centuries that a more specific "language of crusading" emerged. Pope Innocent III used the term negotium crucis "affair of the cross" for the eastern Mediterranean crusade, but was reluctant to apply crusading terminology to the Albigensian crusade. The Song of the Albigensian Crusade from about 1213 contains the first recorded vernacular use of the Occitan crozada. This term was later adopted into French as croisade and in English as crusade. The modern spelling crusade dates to c. 1760. Sinibaldo Fieschi (the future pope Innocent IV) used the terms crux transmarina for crusades in Outremer against Muslims and crux cismarina for crusades in Europe against other enemies of the church.
The Crusades in the Holy Land are traditionally counted as nine distinct campaigns, numbered from the First Crusade of 1095–99 to the Ninth Crusade of 1271–72. This convention is used by historian Charles Mills in his History of the Crusades for the Recovery and Possession of the Holy Land (1820) and is often retained for convenience even though it is somewhat arbitrary. The Fifth and Sixth Crusades led by Holy Roman Emperor Frederick II may be considered a single campaign, as can the Seventh Crusade and Eighth Crusade led by King Louis IX.
The Arabic loanword Muslim is first attested in English in the 17th century. Before this the common term for Muslim was Saracen, in origin referring to the pre-Islamic, non-Arab inhabitants of the desert areas around the Roman province of Arabia. The term evolved to include Arab tribes, and by the 12th century it was an ethnic and religious marker in Medieval Latin literature corresponding to modern "Muslim".
Frank and Latin were used during the Crusades for western Europeans, distinguishing them from Greeks. Crusader sources used the term Syrians to describe Arabic speaking Christians who were members of the Greek Orthodox Church and Jacobites for those who were members of the Syrian Orthodox Church
The term used in modern Arabic, ḥamalāt ṣalībiyya حملات صليبية, lit. "campaigns of the cross", is a loan translation of the term Crusade as used in western historiography.
Christianity was adopted throughout the Roman Empire in Late Antiquity. Following the foundation of the Islamic religion by Muhammad in the 7th century, and continuing through the 8th century, Muslim Arabs under the Umayyad Caliphate captured Syria, Egypt, Iran and North Africa from the Byzantine Empire, and Iberia from the Visigothic Kingdom. In 750 a bloody coup brought an end to Umayyad rule, leading to the gradual fragmentation of the monolithic Islamic state and the relocation of the political and economic centre of the Islamic world to Iran and Iraq and away from Palestine.
By the period leading up to the crusades at the end of the 11th century the age of Islamic territorial expansion was long gone. However, occasionally fractious frontier conditions between the Christian and Muslim world remained across the Mediterranean Sea. From the 8th century, the Christians were campaigning to take Spain in what has become known as the Reconquista, and Norman adventurers led by Norman nobleman Roger de Hauteville (Roger I of Sicily) conquered the Muslim Emirate of Sicily. The territory around Jerusalem had been under Arab Muslim control for more than four centuries, during which levels of tolerance, trade, and political relationships between the Muslims and the Christians fluctuated. Catholic pilgrims had access to sacred sites and Christian residents in Muslim territories were given Dhimmi status, legal rights, and legal protection. Indigenous Christians were also allowed to maintain churches, and marriages between faiths were not uncommon.
The Orthodox Christian Byzantine Empire of Constantinople reached a zenith in early 11th century. The Empire's frontiers were extended east to Iran. In the west control was exerted over Bulgaria and much of southern Italy. However, from this point the arrival of new enemies on all frontiers placed intolerable strains on the resources, both of the Empire and the neighbouring Arab Muslim regimes. This made the Byzantines susceptible to the opportunity presented by western military aid from the Papacy for specific campaigns. In the rising lawlessness the Shi'ite Eqyptian Fatimid dynasty recaptured Jerusalem from the Sunni Seljuqs.
The western chronicles present the First Crusade as a surprising and unexpected event, but historical analysis has demonstrated it was enabled by a number of earlier developments in the 11th century. The city of Jerusalem had become more recognised by both laity and clerics as symbolic of penitential devotion. There is evidence that segments of the western nobility were willing to accept a doctrine of papal governance in military matters. The Seljuq hold on the holy city was weak and the Byzantines were open to the opportunity presented by western military aid for specific campaigns against the Seljuqs. This presented the papacy with a chance to reinforce the principle of papal sovereignty with a display of military power such as that which was proposed by Pope Gregory VII in 1074 but not followed through. Warfare was endemic in Western Europe in this period with violence often a part of political discourse. Contemporaries recognised the moral danger which the papacy attempted to deal with by permitting or even encouraging certain types of warfare. However, the Christian population had a desire for a more effective church which evidenced itself in rioting in Italy and a greater general level of piety. This prompted investment and growth in monasteries across England, France and Germany. Pilgrimage to the Holy Land began in the fourth century but expanded after safer routes through Hungary developed from 1000. It was an increasingly articulate piety within the knighthood and the normative devotional and penitential practises of the aristocracy that created a fertile ground for crusading appeals. The motivations of the First Crusade also included a "messianism of the poor" inspired by an expected mass ascension into heaven at Jerusalem.
Prior to the mid 11th century Gregorian Reform, rival Roman noble families and the Holy Roman Emperor competed to control a Papacy that amounted to little more than a localised bishopric. The Roman families appointed relatives and protégés as popes, while Emperor Henry III invaded Rome and replaced two rival candidates with his own nominee. The reforming movement coalesced around Pope Leo IX, intent on the abolition of simony and clerical marriage along with the implementation of a college of cardinals responsible for the election of future popes. This movement established an assertive, reformist papacy eager to increase its power and influence over secular Europe. A struggle for power developed between Church and state in medieval Europe from around 1075 and continued through the period of the First Crusade. Primarily, this was about whether the Catholic Church or the Holy Roman Empire held the right to appoint church officials and other clerics. This struggle is now known as the Investiture Controversy. In order to gather military resources for his conflict with the Emperor, Pope Alexander II developed a system of recruitment via oaths that Pope Gregory VII extended into a network across Europe. This also supported the development of a doctrine of holy war developed from the thinking of 3rd and 4th century theologian Augustine of Hippo on the treatment of heresy. Death in a just war became to be seen as martyrdom and warfare itself as a penitential activity. Gregory's doctrine of papal primacy led to conflict with eastern Christians where the traditional view was that the Pope was only one amongst the five patriarchs of the church alongside the Patriarchates of Antioch, Constantinople, Alexandria and Jerusalem. Ultimately this led to East–West Schism, the name now given to the split in the Christian church between the Latin west and the Orthodox east in 1054.
In the eastern Mediterranean the arrival of the Seljuqs between the 1040s and 1060s disrupted the status quo. A Turkish tribe recently converted to Islam, the Seljuqs followed the Sunni tradition which quickly brought them into conflict with the Shi'ite Fatimid dynasty, who had ruled Egypt since 969. The Fatimids were independent of the Sunni Abbasid rulers in Baghdad and had a rival Shi'ite caliph, considered the successor to the Muslim prophet Mohammad. However, the conquered indigenous Arabs had lived under the Seljuqs in relative peace and prosperity. In 1092 that relative stability began to disintegrate following the death of the vizier and effective ruler, Nizam al-Mulk, closely followed by the deaths of the Sultan, Malikshah, and the Fatimid khalif, Al-Mustansir Billah. The Islamic historian Carole Hillebrand has described this as analogous to the fall of the Iron Curtain in 1989 with the phrase 'familiar political entities gave way to disorientation and disunity'. The confusion meant the Islamic world disregarded the world beyond; this caused it to be vulnerable to, and surprised by, the First Crusade.
Through military successes under Emperor Basil II, the Byzantine Empire had reached a zenith in 1025. Its frontiers stretched as far east as Iran; it controlled Bulgaria as well as much of southern Italy and piracy had been suppressed in the Mediterranean Sea. However, from this point the arrival of new enemies on all frontiers placed intolerable strains on the resources of the state. In Italy they were confronted by the Normans; to the north the Pechenegs, the Serbians and the Cumans, as well as the Seljuqs. Romanos IV Diogenes attempted to confront the Seljuqs to suppress sporadic raiding; this led to the 1071 defeat of the Byzantine army at the Battle of Manzikert. Once considered a pivotal event by historians, Manzikert is now regarded as only one further step in the expansion of the Great Seljuk Empire into Anatolia. This situation was probably the cause of instability in the Byzantine hierarchy rather than the result. In order to maintain order, the Emperors were forced to recruit mercenary armies, sometimes from the very forces that provided the threat. Yet recent scholarship has identified encouragingly positive signs in the overall health of the Empire.
In the eastern Mediterranean
First Crusade (1096–1099) and aftermath
In 1095, Byzantine Emperor Alexios I Komnenos requested military aid from Pope Urban II, probably in the form of a small body of mercenary reinforcements he could direct and control. Alexios had restored the Empire's finances and authority, but he still faced a number of foreign enemies, particularly the migrating Turks who had colonised the sparsely populated areas of Anatolia Later that year at the Council of Clermont, Urban raised the issue again and preached for a Crusade.
Almost immediately, the French priest Peter the Hermit led thousands of mostly poor Christians out of Europe in what became known as the People's Crusade. In transit through Germany these Crusaders massacred Jewish communities in what became known as the Rhineland massacres as part of wide-ranging anti-Jewish activity, extending from limited, spontaneous violence to full-scale military attacks. Jews were perceived to be as much an enemy as Muslims: they were held responsible for the crucifixion, and they were more immediately visible than the distant Muslims. Many people wondered why they should travel thousands of miles to fight non-believers when there were already non-believers closer to home. The Crusaders then journeyed to Nicaea before a Turkish ambush at Civetot left only 3000 survivors.
Conflict with Urban meant that King Philip I of France and Emperor Henry IV declined to participate in the crusade. But members of the high aristocracy from France, western Germany, the Low countries, and Italy led their own military contingents in loose, fluid arrangements based on bonds of lordship, family, ethnicity, and language. Foremost amongst these was the elder statesman, Raymond IV, Count of Toulouse. He was rivalled by the relatively poor but martial Bohemond of Taranto and his nephew Tancred from the Norman community of southern Italy. They were joined by Godfrey of Bouillon and his brother Baldwin and forces from Lorraine, Lotharingia, and Germany. These five princes were pivotal to the campaign, which was also joined by a northern French army led by Robert Curthose, Stephen, Count of Blois, and Robert II, Count of Flanders. The armies, which may have contained as many as 100,000 people including non-combatants, travelled eastward by land to Byzantium where they were cautiously welcomed by the Emperor. Alexios persuaded many of the princes to pledge allegiance to him; he also convinced them that their first objective should be Nicaea, the capital of the Sultanate of Rum. The over-confident Sultan left the city to resolve a territorial dispute, thus enabling its capture after a Crusader siege and a Byzantine naval assault. This was a high point in Latin and Greek co-operation and the beginning of Crusader attempts to take advantage of disunity in the Muslim world.
The first experience of Turkish tactics, using lightly armoured mounted archers, occurred when an advanced party led by Bohemond and Robert were ambushed at Dorylaeum. The Normans resisted for hours before the arrival of the main army caused a Turkish withdrawal. Factionalism amongst the Turks after the death of Malik Shah, the Sultan of the Seljuq Empire, meant they did not present a united opposition. Instead, Aleppo and Damascus had competing rulers. The three-month march to the Muslim city of Antioch was arduous. Numbers were reduced by starvation, thirst, and disease, combined with the decision of Baldwin to leave with 100 knights and their followers in order to carve out his own territory in Edessa. The Crusaders beseiged the city for eight months but lacked the resources to fully invest the city and the residents lacked the resources to repel the invaders. Finally, Bohemond persuaded a guard in the city to open a gate and the Crusaders entered, massacring the Muslim and many Christian inhabitants amongst the Greek Orthodox, Syrian and Armenian communities.
A force to recapture the city was raised by the Iraqi general Kerbogha. The Byzantines provided no assistance to the Crusaders' defence of the city because the deserting Stephen of Blois told them the cause was lost. Losing numbers through desertion and starvation in the besieged city, the Crusaders attempted to negotiate surrender, but were rejected. Bohemond recognised that the only option now was for open combat, and launched a counterattack. Despite superior numbers, Kerbogha's army, which was divided into factions and surprised by the commitment and dedication of the Franks, retreated and abandoned the siege. The Crusaders then delayed for months while they argued over who would have the captured territory. Debate ended when news arrived that the Fatimid Egyptians had taken Jerusalem from the Turks, making it imperative to attack before the Egyptians could consolidate their position. Bohemond remained in Antioch, retaining the city despite his pledge to return it to Byzantine control, while Raymond led the remaining Crusader army rapidly south along the coast to Jerusalem.
An initial attack on the city failed and the siege became a stalemate. However, the arrival of craftsman and supplies transported by the Genoese to Jaffa tilted the balance. Crusaders constructed two large siege engines; the one commanded by Godfrey breached the walls. For two days the Crusaders massacred the inhabitants and pillaged the city. Historians now believe the accounts of the numbers killed have been exaggerated, but this narrative of massacre did much to cement the Crusaders' reputation for barbarism. Godfrey further secured the Frankish position by defeating an Egyptian relief force at Ascalon. Now, most of the Crusaders considered their pilgrimage complete and returned to Europe. Godfrey was left with a mere 300 knights and 2,000 infantry to defend Palestine. Of the other princes, only Tancred remained with the ambition to gain his own princedom.
The Islamic world seems to have barely registered the Crusade; certainly there is limited written evidence before 1130. This may be in part due to a reluctance to relate Muslim failure, but it is more likely to be the result of cultural misunderstanding. Al-Afdal and the Muslim world mistook the Crusaders for the latest in a long line of Byzantine mercenaries rather than religiously motivated warriors intent on conquest and settlement. The Muslim world was divided between the Sunnis of Syria and Iraq and the Shia Fatimids of Egypt. Even the Turks were divided, with rival rulers in Damascus and Aleppo. In Baghdad the Seljuk sultan, Barkiyaruq, vied with an Abbasid caliph, Al-Mustazhir, in a Mesopotamian struggle. This gave the Franks a crucial opportunity to consolidate without any pan-Islamic counter-attack.
Under the papacies of successive Popes, smaller groups of Crusaders continued to travel to the eastern Mediterranean to fight the Muslims and aid the Crusader States in the early 12th century. The third decade saw campaigns by French nobleman Fulk V of Anjou, the Venetians, and King Conrad III of Germany, as well as the foundation of the Knights Templar, a military order of warrior monks which became international and widely influential. The Templars provided the Crusader States with a standing army that is estimated to have formed half of the states' military forces. The period also saw the innovation of granting indulgences to those who opposed papal enemies. This marked the beginning of what historians call political Crusades.
After a delay of several years the loss of Edessa in 1144 to Imad ad-Din Zengi, governor of Mosul, prompted preaching for what subsequently became known as the Second Crusade. Initially, support was sluggish, partly because Pope Eugenius III delegated the preaching. Bernard of Clairvaux spread the vision that the loss was the result of sinfulness, and redemption was the reward for crusading. Simultaneously, the anti-Semitic preaching of a Cistercian monk called Rudolf initiated massacres of Jews in the Rhineland. This formed part of a general increase in crusading activity, including in Iberia and northern Europe.  For the first time ruling monarchs were campaigning—King Louis VII and Conrad III— but the crusade was not a success. Edessa had been completely destroyed, making its recovery impossible, and the crusade objectives were unclear. Hostility developed between the French and the Byzantines, with the French blaming the Byzantines for defeats suffered against the Seljuks in Anatolia, while the Byzantines laid claims on future territorial gains in northern Syria. As a result, in a decision historians now criticise, the crusaders decided to attack their traditional allies in Damascus. Bad luck, poor tactics and a feeble five-day siege led to internal arguments; the barons of Jerusalem withdrew support and the Crusaders retreated before the arrival of a relief army led by Zengi’s sons. According to William of Tyre, writing thirty years later, from that point the situation of the Latins deteriorated. Historians recognise that morale fell, that distrust developed between the settlers and the crusaders, and that there was also hostility with the Byzantines.
The rise of systemic and murderous political intrigue in Egypt led to the deposition of the vizier, Shawar, and encouraged King Baldwin III of Jerusalem to plan an invasion. The invasion was only halted by Egypt's tribute of 160,000 gold dinars. In 1163 Shawar visited Zengi's son and successor Nur ad-Din in Damascus, seeking political and military support. Some historians have considered Nur ad-Din's support was a visionary attempt to surround the Crusaders, but in practice he prevaricated, only responding when it became clear that the Crusaders might gain an unassailable foothold on the Nile. Nur ad-Din sent his Kurdish general, Shirkuh, who stormed Egypt and restored Shawar. However, Shawar asserted his independence and allied with Baldwin's brother and successor King Amalric. When Amalric broke the alliance in a ferocious attack, Shawar again requested military support from Syria, and Shirkuh was sent by Nur ad-Din for a second time. Amalric retreated, but the victorious Shirkuh had Shawar executed and was appointed vizier. Barely two months later Shirkuh died; he was succeeded by his nephew, Yusuf ibn Ayyub, who became known by his honorific 'Salah al-Din' ('the goodness of faith') and which has been westernised as Saladin. Nur ad-Din died in 1174, the first Muslim to unite Aleppo and Damascus in the Crusade era. Assuming control after the death of his overlord Nur al-Din, Saladin had the strategic choice of establishing Egypt as an autonomous power or attempting to become the pre-eminent Muslim in the eastern Mediterranean; he chose the latter.
As Nur al-Din's territories became fragmented after his death, Saladin legitimised his ascent by positioning himself as a defender of Sunni Islam subservient to both the Caliph of Baghdad and to Nur al-Din's son and successor, As-Salih Ismail al-Malik. In the early years of his ascendency, he seized Damascus and much of Syria, but not Aleppo. After building a defensive force to resist a planned attack by the Kingdom of Jerusalem that never materialised, his first contest with the Latin Christians was not a success. His overconfidence and tactical errors led to defeat at the Battle of Montgisard. Despite this setback, Saladin established a domain stretching from the Nile to the Euphrates through a decade of politics, coercion, and low-level military action. After a life-threatening illness early in 1186, he determined to make good on his propaganda as the champion of Islam, embarking on heightened campaigning against the Latin Christians. King Guy responded by raising the largest army that Jerusalem had ever put into the field. However, Saladin lured the force into inhospitable terrain without water supplies, surrounded the Latins with a superior force, and routed them at the Battle of Hattin. Guy was amongst a number of Christian nobles taken prisoner but later released. Saladin offered the Christians the option of remaining in peace under Islamic rule or taking advantage of 40 days' grace to leave. As a result of his victory, much of Palestine quickly fell to Saladin, including—after a short five-day siege—Jerusalem. According to Benedict of Peterborough, Pope Urban III died of deep sadness on 19 October 1187 on hearing of the defeat.
Urban III's successor as Pope, Gregory VIII, issued a papal bull titled Audita tremendi that proposed what became known as the Third Crusade to recapture Jerusalem. In August 1189, the freed king Guy attempted to recover Acre from Saladin by surrounding the strategic city, only for his own forces to be besieged in turn. Both armies could be supplied by sea so a long stalemate commenced. However, the Crusaders became so deprived at times they are thought to have resorted to cannibalism. Travelling overland to join the crusade, Holy Roman Emperor Frederich I drowned in the Saleph River; few of his men reached their destination. Richard the Lionheart, King of England, travelled by sea; his sister and his fiancée were travelling separately. In response to their capture by the island's ruler, Isaac Komnenos, Richard conquered Cyprus in 1191. Philip II of France was the first king to arrive at the siege of Acre; Richard arrived on 8 June 1191. The arrival of the French and Angevin forces turned the tide in the conflict, and the Muslim garrison of Acre finally surrendered on 12 July. Philip considered his vow fulfilled and returned to France to deal with domestic matters, leaving most of his forces behind. But Richard travelled south along the Mediterranean coast, defeated the Muslims near Arsuf, and recaptured the port city of Jaffa. He twice advanced to within a day's march of Jerusalem, but judging that—while Saladin had a mustered army—Richard himself lacked the resources to successfully capture the city or to defend it in the unlikely event of a successful assault. This marked the end of Richard's crusading career and was a calamitous blow to Frankish morale. A three-year truce was negotiated that allowed Catholics unfettered access to Jerusalem. Politics in England as well as illness forced Richard's departure, never to return; Saladin died in March 1193. Emperor Henry VI initiated the German Crusade to fulfil the promises to undertake a Crusade to the Holy Land made by his father Frederick. Led by Conrad, Archbishop of Mainz, the army captured the cities of Sidon and Beirut. However, in 1197 Henry died and most of the Crusaders returned to Germany to protect their holdings and take part in the election of his successor as Emperor.
Pope Innocent III began preaching what became the Fourth Crusade in 1200, primarily in France but also in England and Germany. This Crusade was diverted by the Doge, the ruler of Venice elected by members of the Grand Council, Enrico Dandolo and King Philip of Swabia to further their aggressive territorial objectives. Dandolo aimed to expand Venice's power in the eastern Mediterranean, and Philip intended to restore his exiled nephew, Alexios IV Angelos, along with Angelos's father, Isaac II Angelos, to the throne of Byzantium. This would require overthrowing the present ruler, Alexios III Angelos, the uncle of Alexios IV. The Crusaders were unable to pay the Venetians for a fleet so they agreed to divert the Crusade to attack Constantinople and share what could be looted as payment. The Crusaders seized the Christian city of Zara as collateral; Innocent was appalled, and promptly excommunicated them. After the Crusades took Constantinople for a first time, the original purpose of the campaign was defeated by the assassination of Alexios IV Angelos. As a result, the Crusaders attacked the city for a second time and this time sacked it which involved the pillaging of churches and the killing many of the citizens. The result was that the Fourth Crusade never came within 1,000 miles of its objective of Jerusalem.
The 13th century saw a new military threat to the Christian and Isalamic worlds as the Mongols swept east from Mongolia through southern Russia, Poland and Hungary while also defeating the Seljuks and threatening the Crusader states. Separately, Europe saw popular outbursts of ecstatic piety in support of the Crusades, such as that resulting in the Children's Crusade in 1212. Large groups of young adults and children spontaneously gathered, believing their innocence would enable success where their elders had failed. Few, if any at all, journeyed to the eastern Mediterranean. Although little reliable evidence survives for these events, they provide an indication of how hearts and minds could be engaged for the cause.
Following Innocent III's Fourth Lateran Council, crusading resumed in 1217 against Saladin's Ayyubid successors in Egypt and Syria for what is classified as the Fifth Crusade. Led by King Andrew II of Hungary and Leopold VI, Duke of Austria, forces drawn mainly from Hungary, Germany, Flanders, and Frisia achieved little. Leopold and John of Brienne, the King of Jerusalem and later Latin Emperor of Constantinople, besieged and captured Damietta but an army advancing into Egypt was compelled to surrender. Damietta was returned and an eight-year truce agreed. Emperor Frederick II was excommunicated for breaking a treaty obligation with the Pope that required him to lead a crusade. However, since his marriage Isabella II of Jerusalem, John of Brienne's daughter and heir, gave him a claim to the kingdom of Jerusalem, he finally arrived at Acre in 1228. Frederick was culturally the Christian monarch most empathetic to the Muslim world, having grown up in Sicily, with a Muslim bodyguard and even a harem. His great diplomatic skills meant that the Sixth Crusade was largely negotiation supported by force. A peace treaty was agreed upon, giving Latin Christians most of Jerusalem and a strip of territory that linked the city to Acre, while the Muslims controlled their sacred areas. In return, an alliance was made with Al-Kamil, Sultan of Egypt, against all of his enemies of whatever religion. The treaty and suspicions about Frederick's ambitions in the region made him unpopular, and he was forced to return to his domains when they were attacked by Pope Gregory IX. While the Holy Roman Empire and the Papacy were in conflict, it often fell to secular leaders to campaign. What is sometimes known as the Barons' Crusade was led by Count Theobald I of Navarre and Earl Richard of Cornwall; it combined forceful diplomacy and the playing of rival Ayyubid factions off against each other. This brief renaissance for Frankish Jerusalem was illusory, being dependent on Ayyubid weakness and division following the death of Al-Kamil.
13th-century politics in the eastern Mediterranean were complex, with a number of powerful interested parties. The French were led by the very devout King Louis IX, king of France and his ambitious brother Charles who was keen to expand his secular territories. With the support of the papacy, Charles seized Sicily and Byzantine territory while using more peaceful means to expand his influence through the marriage of his daughters to the Latin claimants to Byzantium. In addition he executed one rival and purchased the rights to the city from another to create his own claim to the throne of Jerusalem. In 1244 a band of Khwarezmian mercenaries travelling to Egypt to serve As-Salih Ismail, Emir of Damascus, seemingly of their own volition, captured Jerusalem en route and defeated a combined Christian and Syrian army at the Battle of La Forbie. Louis responded by organising a Crusade, called the Seventh Crusade, to attack Egypt, arriving in 1249. Louis was defeated at Mansura and captured as he retreated to Damietta. Another truce was agreed upon for a ten-year period, and Louis was ransomed. Louis remained in Syria until 1254 to consolidate the Crusader states. From 1265 to 1271, the Mamluk sultan Baibars drove the Franks to a few small coastal outposts. Baibars had three key objectives: to prevent an alliance between the Latins and the Mongols, to cause dissension between the Mongols (particularly between the Golden Horde and the Persian Ilkhanate), and to maintain access to a supply of slave recruits from the Russian steppes. In this, he supported King Manfed of Sicily's failed resistance to the attack of Charles and the Papacy. Dissention in the Crusader states led to conflicts such as the War of Saint Sabas. Venice drove the Genoese from Acre to Tyre where they continued to trade happily with Baibars' Egypt. Indeed, Baibars negotiated free passage for the Genoese with Michael VIII Palaiologos, Emperor of Nicaea, the newly restored ruler of Constantinople.
In 1270 Charles turned his brother King Louis IX's crusade, known as the Eighth, to his own advantage by persuading Louis to attack his rebel Arab vassals in Tunis. The crusader army was devastated by disease, and Louis himself died at Tunis on 25 August. The fleet returned to France. Prince Edward, the future king of England, and a small retinue arrived too late for the conflict but continued to the Holy Land in what is known as the Ninth Crusade. Edward survived an assassination attempt, negotiated a ten-year truce, and then returned to manage his affairs in England. This ended the last significant crusading effort in the eastern Mediterranean. The 1281 election of a French pope, Martin IV, brought the full power of the papacy into line behind Charles. He prepared to launch a crusade against Constantinople but, in what became known as the Sicilian Vespers, an uprising fomented by the Byzantine Emperor Michael deprived him of the resources of Sicily and Peter III of Aragon was proclaimed king. In response, Martin excommunicated Peter and called for an Aragonese Crusade, which was unsuccessful. In 1285 Charles died bringing to an end a period when he and his brother King, later Saint, Louis had viewed themselves as God's instruments to uphold the papacy. He had spent his life in the attempt to amass a Mediterranean empire.
The causes of the decline in Crusading and the failure of the Crusader States is multi-faceted. Historians have attempted to explain this in terms of Muslim reunification and Jihadi enthusiasm but Thomas Asbridge, amongst others, considers this too simplistic. Muslim unity was sporadic and the desire for Jihad ephemeral. The nature of Crusades was unsuited to the conquest and defence of the Holy Land. Crusaders were on a personal pilgrimage and usually returned when it was completed. Although the philosophy of Crusading changed over time, the Crusades continued to provide short-lived armies without centralised leadership led by independently minded potentates. What the Crusader states needed were large standing armies. Religious fervour enabled significant feats of military endeavour but proved difficult to direct and control. Succession disputes and dynastic rivalries in Europe, failed harvests and heretical outbreaks, all contributed to reducing Latin Europe's concerns for Jerusalem. Ultimately, even though the fighting was also at the edge of the Islamic world, the huge distances made the mounting of Crusades and the maintenance of communications insurmountably difficult. It enabled the Islamic world, under the charismatic leadership of Nur al-Din and Saladin, as well as the ruthless Baibars, to use the logistical advantages from proximity to victorious effect. The mainland Crusader states of the Outremer were finally extinguished with the fall of Tripoli in 1289 and Acre in 1291. Many Latin Christians were evacuated to Cyprus by boat, were killed or enslaved, however 16th-century Ottoman census records of Byzantine churches show that most parishes remained Christian throughout the Middle Ages.
The success of the First Crusade led to further and multifaceted crusading in the Middle Ages. The Western Europeans developed a different, overtly spiritual, perception of the reconquest of the Iberian Peninsula. Other conflicts began to be seen as Crusades with Crusading privileges and legal frameworks applied. These conflicts, outside the Holy Land, included the territorial wars in the Baltic, the Popes' wars against their political enemies in Italy and, after the Fourth Crusade, the defence of the Latin Empire of Constantinople.
At the time of the First Crusade, Spain was the only example of Latin Christians subjugated by the Islamic World. The period of conquest was over by c. 900 and in 1031 the collapse of the Caliphate of Córdoba created the political conditions that would make the Reconquista possible. The Christian powers—León, Navarre, Aragon and Catalonia—were essentially geo-political constructs with no history based on tribe or ethnicity. Although small, all had developed a military aristocracy and technique. By the time of the Second Crusade three kingdoms had developed enough to represent Christian expansion—Castile and León, Aragon and Portugal. A consensus has emerged among modern historians against the view of a generation of Spanish scholars who believed it was Spanish religious and national destiny to defeat Islam. In 1123 Calixtus II issued a Bull creating an equivalence between the Reconquista and crusading in the east against Muslims. However, it was the Second Crusade that placed it within the context of Crusading. Pope Eugenius III followed naming Iberia as a target, the Genoese provided logistic support, a mixed band of Crusaders captured Lisbon and Bernard of Clairveaux preached for the campaign in the same terms as he did against the Wends of Denmark. The Battle of Las Navas de Tolosa was won in 1212 with the support of 70,000 non-Spanish combatants responding to a crusade preached by Innocent III. However, many of these deserted because of the toleration the Spanish demonstrated to the defeated Muslims. For the Spanish, The Reconquista was a war of domination rather than extinction. This contrasted with the treatment of the native Christians, the Mozarabs. The Roman Rite was relentlessly imposed and the native Christians were absorbed into mainstream the Roman church by the Cistercians, Cluniac clerical appointments and the Military Orders. The Reconquista was not immediately completed and continued to attract crusaders and crusader privileges until Al-Andalus was suppressed in the Fourteenth century. The Emirate of Granada held out until 1492, at which point the Muslims and Jews were finally expelled from the peninsula.
At the Third Council of the Lateran in 1179, Pope Innocent III set a different precedent relevant to those crusades that were and are considered as political. In this he encouraged those who defended Christendom against heretics by the offering of indulgances. Although the lack of priority given to the campaign against the Cathers in southern France can be seen in the comparison between the thirty-year delay in instigating the Albigensian Crusade compared with the more immediate response in crusading rhetoric regarding the Papacy territorial conflicts in Italy. The Albigensian Crusade taught the Papacy that it was in fact far easier to attack those who provided a home for heresy rather than to identify and eradicate the heresy itself. Examples of this include threatening Milan on the grounds they tolerated Catharism and in Languedoc confiscating the lands of lords who failed in its suppression. The historian Housley notes the strong political undertones and connection between heterodoxy and anti-papalism. The Pope and the Inquisition would claim that anyone not with them was against them and label opponents as Cathars without requiring evidence. Indulgances were offered to anti-heretical groups such as the Militia of Jesus Christ and the Society of the Blessed Virgin in Milan.
The initial indication the papacy would begin to regard the Northern Crusades—wars waged by Scandinavian and German Christians against the pagans indigenous to the Baltic coastal region—came in 1147 with Bernard of Clairvaux persuading Pope Eugenious III that the conflict with the Wends was a holy war analogous to the Reconquista. However, this was recognition of the fact that the Germans were more motivated by wars of territorial conquest than events in the east. This Wendish Crusade saw Saxons, Danes, and Poles begin to forcibly convert the tribes of Mecklenburg and Lusatia, who were Polabian Slavs or "Wends". This, and further campaigns against Estonian and Finnish pagans were understood in religious terms by contemporaries as a struggle against paganism. However, the theoretical justification was uncertain without the argument that the crusaders were fighting to reclaim Christian territory, mass conversion was implausible and destruction of the pagans counter productive.
Military orders played a controversial role in the Baltic, most notably the Teutonic Knights who were founded in Palestine after the siege of Acre and modelled on the Templars. The orders strong links to German Imperium diverted efforts from the Holy Land to Prussia and Livonia. Other orders redated the Knights such as the Livonian Brothers of the Sword and the Order of Dobrzyń who were founded to defend Riga and German commercial interests. This they did with the harsh and brutal suppression of the local populations, including Orthodox Christians. In this way Latin control was extended 300 miles to the east in the 13th century. The historian Robert Bartlett defines the conquest and organisation of power in the Baltic as part of a general movement for 'the expansion of Latin Christendom'. It was made possible by the crusading ideology placing the full machinary of the Church behind superior military technology. It enabled the recruitment of troops via preaching, the offer of spriritual rewards for combatants and the administrative machinary to establish government in the conquered territories.
During the Late Middle Ages and Early Modern Period
Minor Crusading efforts lingered into the 14th century, and several Crusades were launched during the 14th and 15th centuries to counter the expansion of the Ottoman conquest of the Balkans. In 1309 as many as 30,000 peasants gathered from England, north-eastern France, and Germany proceeded as far as Avignon but disbanded there. King Peter I of Cyprus captured and sacked Alexandria in 1365 in what became known as the Alexandrian Crusade; his motivation was as much commercial as religious. Louis II led the 1390 Barbary Crusade against Muslim pirates in north Africa; after a ten-week siege, the Crusaders signed a ten-year truce.
The Ottomans had conquered most of the Balkans and reduced Byzantine influence to the area immediately surrounding Constantinople after victory at the Battle of Kosovo in 1389. Nicopolis was seized from the Bulgarian Tsar Ivan Shishman in 1393 and a year later Pope Boniface IX proclaimed a new Crusade against the Turks, although the Western Schism had split the papacy. This Crusade was led by Sigismund of Luxemburg, King of Hungary; many French nobles joined Sigismund's forces, including the Crusade's military leader, John the Fearless (son of the Duke of Burgundy). Sigismund advised the Crusaders to adopt a cautious, more defensive strategy, when they reached the Danube, instead they besieged the city of Nicopolis. The Ottomans defeated them in the Battle of Nicopolis on 25 September, capturing 3,000 prisoners.
The Hussite Wars, also known as the Hussite Crusade, involved military action against the Bohemian Reformation in the Kingdom of Bohemia and the followers of early Czech church reformer Jan Hus, who was burned at the stake in 1415. Crusades were declared five times during that period: in 1420, 1421, 1422, 1427, and 1431. These expeditions forced the Hussite forces, who disagreed on many doctrinal points, to unite to drive out the invaders. The wars ended in 1436 with the ratification of the compromise Compacts of Basel by the Church and the Hussites.
As the Ottomans pressed westward, Sultan Murad II destroyed the last Papal-funded Crusade at Varna on the Black Sea in 1444 and four years later crushed the last Hungarian expedition. In 1453 they extinguished most of the remains of the Byzantine Empire with the capture of Constantinople. John Hunyadi, a Hungarian general, and the Franciscan friar Giovanni da Capistrano organised a 1456 Crusade to oppose the Ottoman Empire and lift the Siege of Belgrade. Æneas Sylvius, the future Pope Pius II, and John of Capistrano, the future Saint John of Capistrano, preached the Crusade. The princes of the Holy Roman Empire in the Diets of Ratisbon and Frankfurt promised assistance, and a league was formed between Venice, Florence, and Milan, but eventually nothing came of it. In April 1487 Pope Innocent VIII called for a Crusade against the Waldensians of Savoy, the Piedmont, and the Dauphiné in southern France and northern Italy because they were unorthodox and heretical. The only efforts undertaken were in the Dauphiné, resulting in little change. Venice was the only polity to continue to pose a significant threat to the Ottomans in the Mediterranean, but it pursued the "Crusade" mostly for its commercial interests, leading to the protracted Ottoman–Venetian Wars, which continued, with interruptions, until 1718. The end of the Crusading in terms of at least nominal efforts by Catholic Europe against Muslim incursion, came in the 16th century, when the Franco-Imperial wars assumed continental proportions. King Francis I of France sought allies from all quarters, including from German Protestant princes and Muslims. Amongst these, he entered into one of the capitulations of the Ottoman Empire with Ottoman Sultan Suleiman the Magnificent while making common cause with Hayreddin Barbarossa, an Ottoman admiral, and a number of the Sultan's north African vassals.
After the First Crusade's capture of Jerusalem and victory at Ascalon the majority of the Crusaders considered their personal pilgrimage complete and returned to Europe. Godfrey found himself left with only 300 knights and 2,000 infantry to defend the territory won in the eastern Mediterranean. Of the crusader princes, only Tancred remained with the aim of establishing his own lordship. At this point the Franks held Jerusalem and two great Syrian cities – Antioch and Edessa – but not the surrounding country. Jerusalem remained economically sterile despite the advantages of being the centre of administration of church and state and benefiting from streams of pilgrims. Modern research based on historical geography techniques indicate that the spatial distribution of Muslims and indigenous Christians was more sharply delineated than previously thought. Palestinian Christians lived around Jerusalem and in an arc stretching from Jericho and the Jordan to Hebron in the south. Central Areas appear to be Muslim from the point of the destruction of the Samarian communities in the 6th-century. These communities are now thought to be of nearly equal size, perhaps even in a 50:50 proportion. The Frankish population of the Kingdom of Jerusalem became concentrated in three major cities. By the thirteenth century the population of Tyre probably exceeded 60,000, then came Acre and the capital itself was the smallest of the three numbering between 20,000 and 30,000. At the zenith of the Crusader Kingdoms, the total Latin population of the region reached around 250,000 with the kingdom amounting to about 120,000 and the total combined numbers in Tripoli, Antioch and Edessa being broadly similar.
The "Law of Conquest" supported the seizure of land and property by impecunious Crusaders from the autochthonous population, enabling poor men to become rich and part of the nobility. Although some historians, like Jotischky, question the model once proposed, in which the primary motivation was understood in sociological and economic rather than spiritual terms. The Franks did not distinguish on grounds of religion; the basic division in society was between Frank and non-Frank, rather than between Christian and Muslim. The new Frankish rulers did not expel the native population, but adopted strict segregation and at no point attempted to integrate it by way of religious conversion. In this way the Crusaders created a colonial nobility that perpetuated itself through an incessant flow of religious pilgrims and settlers keen to take economic advantage.
Records preserved from John of Ibelin (jurist) indicate that the military force of the kingdom was based on a feudal host of about 647 to 675 knights in 1170. Each feudatory would also provide his own armed retainers. This force would be augmented by mercenary serjants and John records 5,025 of these. In times of emergency the King could also call upon a general muster of the population. The historian Joshua Prawer estimates that the military orders could match the fighting strength of the king's army meaning that the total military strength of the kingdom was can be estimated at 1,200 knights and 10,000 serjants. This meant that conquest was possible, but ephemeral because of a lack of the numbers to maintain military domination. This demograhic lack of numbers was also a problem defensively as putting an army into the field required the draining of every Crusader castle and city of every able bodied fighting man. In the case of a defeat such as Hittin there remained no one to resist the invaders. Muslim armies were incohesive and seldom campaigned beyond a period between sowing and harvest. As a result, the Crusaders adopted tactics, that when faced with a superior invading Muslim force, in which they would avoid direct confrontation instead retreating to strongholds and waiting for the Muslim army to disperse. It took generations before the Muslims recognised that the destruction of walled cities and castles would end Crusader rule. This strategic change forced the Crusaders into their ultimately unsuccessful strategy of destroying Egypt in order to gain enough time to improve the Kingdom's demographic weakness
The key differentiator in status and economic position in the Crusader States was between urban and rural dwellers. There was no Frankish peasantry, this was a role fulfilled by the native peoples. The Franks imposed their own feudal culture on agricultural production which made little difference in the conditions of the rural population. However, the poll tax on non-Muslims was reversed enabling the feudal Lords to raise punitive levels of revenue from the indigenous peoples, whether Muslim, Jewish or Christian. Very few Muslims lived in urban areas except those in servitude, although indigenous Christians could gain legal status and acquire wealth through commerce and industry in towns.
The territorial gains followed distinct ethnic and linguistic entities. The Principality of Antioch, founded in 1098 and ruled by Bohemond, became Norman in character and custom. The Kingdom of Jerusalem, founded in 1099, followed the traditions of northern France. The County of Tripoli, founded in 1104 (although the city of Tripoli itself remained in Muslim control until 1109) by Raymond de Saint-Gilles became Provençal. The County of Edessa, founded in 1098, differed in that although it was ruled by the French Bouillons and Courteneys its largely Armenian and Jacobite native nobility was preserved. These states were the first examples of "Europe overseas". They are generally known by historians as Outremer, from the French outre-mer ("overseas" in English).
Largely based in the ports of Acre and Tyre, Italian, Provençal and Spanish communes provided a significant characteristic of Crusader social stratification and political organisation. Separate from the Frankish nobles or burgesses, the communes were autonomous political entities closely linked to their countries of origin. This gave the inhabitants the ability to monopolise foreign trade and almost all banking and shipping in the Crusader states. Every opportunity to extend trade privileges was taken. One example saw the Venetians receiving one third of Tyre, its territories and exemption from all taxes, after Venice participated in the successful 1124 siege of the city. However, despite all efforts, the two ports were unable to replace Alexandria and Constantinople as the primary centres of commerce in the region. Instead, the communes competed with the Crown and each other to maintain economic advantage. Power derived from the support of the communards' native cities rather than their number, which never reached more than several hundred. Thus by the middle of the 13th century, the rulers of the communes were barely required to recognise the authority of the crusaders and divided Acre into a number of fortified miniature republics.
The conquest of Christian Constantinople by the Fourth Crusade created a significant increase in the Frankish Crusader presence in the eastern Mediterranean. Those Crusaders that remained established control over the city, Thrace, Greece, the extreme north west of Anatolia as well as the Ionian and Aegean Islands. A council of six Venetians and six Franks selected Count Baldwin of Flanders as a new Latin Emperor. This established a Latin Empire in the east and partitioned the Byzantine territory. The Latin emperor controlled one-fourth of the Byzantine territory, Venice three-eighths (including three-eighths of the city of Constantinople), and the remainder was divided among the other leaders of the Crusade. This period of Greek history is known as the Frankokratia or Latinokratia ("Frankish [or Latin] rule") and designates a period when Catholic Western European nobles, primarily from France and Italy, ruled over the Orthodox Byzantine Greeks on former Byzantine territory.[A] In the long run, the sole beneficiary was Venice.
The Crusaders' mentality to imitate the customs from their Western European homelands meant that there were very few innovations developed from the culture of the crusader states. Three notable exceptions to this rule are the military orders, warfare and fortifications. The Hospitallers (Order of Knights of the Hospital of Saint John of Jerusalem) were founded in Jerusalem before the First Crusade but added a martial element to its ongoing medical functions to become a much larger military order. In this way the knighthood entered the previously monastic and ecclesiastical sphere.
The military orders such as the Knights Hospitaller and Knights Templar provided Latin Christendom's first professional armies in support of the Latin Kingdom of Jerusalem and the other Crusader states. The Poor Knights of Christ (Templars) and their Temple of Solomon were founded around 1119 by a small band of knights who dedicated themselves to protecting pilgrims en route to Jerusalem. The Hospitallers and the Templars became supranational organisations as Papal support led to rich donations of land and revenue across Europe. This in turn led to a steady flow of new recruits and the wealth to maintain multiple fortifications across the Outremer. In time, this developed into autonomous power in the region. After the fall of Acre the Hospitallers first relocated to Cyprus, then conquered and ruled Rhodes (1309–1522) and Malta (1530–1798), and continue in existence to the present day. King Philip IV of France probably had financial and political reasons to oppose the Knights Templar, which led to him exerting pressure on Pope Clement V. The Pope responded in 1312, with a series of papal bulls including Vox in excelso and Ad providam that dissolved the order on the alleged and probably false grounds of sodomy, magic, and heresy.
Art and architecture
According to Joshua Prawer no major European poet, theologian, scholar or historian settled in the Crusader states. A number went on pilgrimage and this is reflected in new imagery and ideas in the important areas of western poetry. Although they did not practice what they preached the output often formed encouragement to journey on pilgrimage to the east. 
Historians consider military architecture — demonstrating a synthesis of the European, Byzantine and Muslim traditions — the most original and impressive artistic achievement of the Crusades. Castles were a tangible symbol of the dominance of a Christian minority over a largely hostile majority population as well as acting as centres of administration. 
Modern historiography rejects the 19th-century consensus that Westerners learnt the basis of military architecture from the Near East as Europe had already experienced rapid growth in defensive technology before the First Crusade. Although, direct contact with Arab fortifications originally constructed by the Byzantines influenced and enriched the development in the east. With the lack of documentary evidence it remains difficult to differentiate between the influences of situation on the inclusion of Oriental design features such as large water reservoirs or the exclusion of Occidental features such as moats. 
It is in the area of visual culture that the assimilated nature of the society was demonstrated. Throughout the 12th and 13th-centuries the influence of indigenous artists was demonstrated in religious architecture, decoration of shrines, painting and the production of manuscripts. Additionally Frankish practitioners borrowed methods from the Byzantines and indigenous artists and iconographical practice. Typically, early church design was in the French Romanesque style. This can be seen in the 12th-century rebuilding of The Church of the Holy Sepulchre which retained some of the Byzantine details but new arches and chapels were built to northern French, Aquitanian and Provencal patterns. In contrast monumental and panel painting, mosaics and illuminations in manuscripts adopt an indigenous style leading to a cultural synthesis illustrated by the Church of the Nativity. Wall mosaics were unknown in the west but in widespread use in the Crusader states. Whether this was by indigenous craftsmen or learnt by Frankish ones is unknown, but a distinctive original artistic style evolved. 
Manuscripts were produced and illustrated in workshops housing Italian, French, English and local craftsmen leading to a cross fertilisation of ideas and techniques. An example of this is the Melisende Psalter created in a workshop attached to the Holy Sepulchre by multiple hands. This style could have reflected or influenced the taste of artistic patrons. But what is seen is an increase in stylised Byzantine influenced content. This even extended to the production of Icons, unknown at the time to the Franks, sometimes in a Frankish style and even of western saints. This is seen as the origin of Italian panel painting. 
The Kingdom of Jerusalem was the first experiment in European colonialism, setting up a "Europe Overseas" or Outremer. The raising, transportation, and supply of large armies led to flourishing trade between Europe and Outremer. The Italian city states of Genoa and Venice flourished, planting profitable trading colonies in the eastern Mediterranean. Some of these communities survived through the middle Byzantine and Ottoman eras. These were often assimilated, with their inhabitants known as Levantines or Franco-Levantines.[B]
The Crusades consolidated the papal leadership of the Latin Church, reinforcing the link between Western Christendom, feudalism, and militarism and increased the tolerance of the clergy for violence. The growth of the system of indulgences became a catalyst for the Reformation in the early 16th century. The Crusades also had a role in the formation and institutionalisation of the military and the Dominican orders as well as of the Medieval Inquisition.
The behaviour of the Crusaders in the eastern Mediterranean area appalled the Greeks and Muslims, creating a lasting barrier between the Latin world and both the Islamic and Orthodox religions. It became an obstacle to the reunification of the Christian church and fostered a perception of Westerners as defeated aggressors. However, many historians argue that the interaction between the western Christian and Islamic cultures played a significant, ultimately positive, part in the development of European civilisation and the Renaissance. Relations between Europeans and the Islamic world stretched across the entire length of the Mediterranean Sea, leading to an improved perception of Islamic culture in the West, but also make it difficult for historians to identify the specific source of cultural cross-fertilisation. The art and architecture of Outremer show clear evidence of influence, but it is difficult to track illumination of manuscripts and castle design back to their sources. Textual sources are simpler, and translations made in Antioch are notable but considered secondary in importance to the works emanating from Muslim Spain and from the hybrid culture of Sicily. Muslim libraries contained classical Greek and Roman texts that allowed Europe to rediscover pre-Christian philosophy, science and medicine.
Historical parallelism and the tradition of drawing inspiration from the Middle Ages have become keystones of Islamic ideology. Secular Arab nationalism highlights the role of Western imperialism. Gamal Abdel Nasser (President of Egypt from 1954 to 1970 and President of the United Arab Republic from 1958 to 1970) likened himself to Saladin and imperialism to the Crusades. In his History of the Crusades (1963) Sa'id Ashur emphasised the similarity between the modern and medieval situation facing Muslims and the need to study the Crusades in depth. Sayyid Qutb (1906–1966) declared there was an international Crusader conspiracy. The ideas of Jihad and of a long struggle have developed some currency. Muslim thinkers, politicians and historians have drawn parallels between the Crusades and modern political developments such as the French Mandate for Syria and the Lebanon, Mandatory Palestine, and the United Nations mandated foundation of the state of Israel. Right-wing circles in the Western world have drawn opposing parallels, considering Christianity to be under an Islamic religious and demographic threat that is analogous to the situation at the time of the Crusades. Crusader symbols and anti-Islamic rhetoric are presented as an appropriate response, even if for only propaganda purposes. These symbols and rhetoric are used to provide a religious justification and inspiration for a struggle against a religious enemy.
By the 16th-century, Western historians saw the Crusades through the lens of their own religious beliefs. While the Protestant viewpoint was they were manifestations of the evils of the papacy, the Catholic view was to see the events as a positive force. The Enlightenment in the 18th-century extended the former to the point that the Middle Ages in general, and the Crusades in particular, were the efforts of barbarian cultures driven by fanaticism. In The History of the Decline and Fall of the Roman Empire, 18th-century English historian Edward Gibbon wrote that the Crusaders' efforts could have been more profitably directed towards improving their own countries.
Jonathan Riley-Smith considers that much of the popular understanding of the Crusades derives from the 19th century novels of Walter Scott and the French histories by Joseph François Michaud. The Crusades provided an enormous amount of source material, stories of heroism, and interest that underpinned growth in medieval literature, romance, and philosophy.
- Traditionalists restrict their definition of the Crusades to the Christian campaigns in the Holy Land, "either to assist the Christians there or to liberate Jerusalem and the Holy Sepulcher", during 1095–1291.
- Pluralists use the term Crusade of any campaign explicitly sanctioned by the reigning Pope. This reflects the view of the Roman Catholic Church (including medieval contemporaries such as Saint Bernard of Clairvaux) that every military campaign given Papal sanction is equally valid as a Crusade, regardless of its cause, justification, or geographic location. This broad definition includes attacks on paganism and heresy such as the Albigensian Crusade, the Northern Crusades, and the Hussite Wars, and wars for political or territorial advantage such as the Aragonese Crusade in Sicily, a Crusade declared by Pope Innocent III against Markward of Anweiler in 1202, one against the Stedingers, several (declared by different popes) against Emperor Frederick II and his sons, two Crusades against opponents of King Henry III of England, and the Christian re-conquest of Iberia.
- Generalists see Crusades as any and all holy wars connected with the Latin Church and fought in defence of the faith.
- Popularists limit the Crusades to only those that were characterised by popular groundswells of religious fervour – that is, only the First Crusade and perhaps the People's Crusade.
The Muslim world exhibited little interest in European culture until the 16th century and in the Crusades until the mid-19th century. There was no history of the Crusades translated into Arabic until 1865 and no published work by a Muslim until 1899. In the late 19th century, Arabic-speaking Syrian Christians began translating French histories into Arabic, leading to the replacement of the term "wars of the Ifranj" – Franks – with al-hurub al Salabiyya – wars of the Cross. Namik Kamel published the first modern Saladin biography in 1872. The Jerusalem visit in 1898 of Kaiser Wilhelm prompted further interest, with Sayyid Ali al-Harri producing the first Arabic history of the Crusades.
- Arab–Byzantine wars (634–1050s)
- Art of the Crusades
- Byzantine–Ottoman Wars (1265–1479)
- Crusade cycle – Old French cycle of epic poems concerning the First Crusade
- The Crusades, An Arab Perspective
- History of the Jews and the Crusades
- List of principal Crusaders
- List of Crusader castles
- Ottoman Wars in Europe (1453–1922)
- Miles Christianus ("Christian soldier")
- The Partitio terrarum imperii Romaniae is a valuable record of early-13th-century Byzantine administrative divisions (episkepsis) and family estates.
- Frankolevantini; French Levantins, Italian Levantini, Greek Φραγκολεβαντίνοι, and Turkish Levantenler or Tatlısu Frenk leri. Later European visitors pejoratively used the term "Levantine" for inhabitants of mixed Arab and European descent and for Europeans who adopted local dress and customs.
- Asbridge 2012, p. 40
- Tyerman 2006, p. 259
- Ghil 1995, pp. 99–109
- "Crusade". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
- Tyerman 2006, p. 480
- Davies 1997, p. 358
- Tolan 2002, p. xv
- Retso 2003, pp. 505–06
- Retso 2003, p. 96
- "Frank". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
- "Latin". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
- Jotischky 2004, p. 141
- Determann 2008, p. 13
- Tyerman 2006, pp. 51–54.
- Asbridge 2012, p. 18
- Jotischky 2004, p. 40
- Mayer 1988, pp. 17–18
- Findley 2005, p. 73
- Jotischky 2004, pp. 42–46
- Jotischky 2004, p. 46
- Asbridge 2012, p. 27
- Jotischky 2004, pp. 41–42
- Asbridge 2012, p. 28
- Jotischky 2004, pp. 35–38
- Cohn 1970, pp. 61, 64
- Jotischky 2004, p. 24
- Jotischky 2004, p. 25
- Rubenstein 2011, p. 18
- Cantor 1958, pp. 8–9
- Jotischky 2004, pp. 26–27
- Jotischky 2004, pp. 27–30
- Mayer 1988, pp. 2–3
- Hillenbrand 1999, p. 33
- Jotischky 2004, pp. 39–41
- Jotischky 2004, p. 41
- Asbridge 2012, p. 34
- Hindley 2004, pp. 20–21
- Chazan 1996, p. 60
- Tyerman 2007, pp. 99–100
- Hindley 2004, p. 23
- Asbridge 2012, pp. 43–47
- Hindley 2004, pp. 30–31
- Asbridge 2012, pp. 52–56
- Asbridge 2012, pp. 57–59
- Asbridge 2012, pp. 21–22
- Asbridge 2012, pp. 59–61
- Asbridge 2012, pp. 72–73
- Asbridge 2012, pp. 72–82
- Asbridge 2012, pp. 146–53
- Asbridge 2012, pp. 96–103
- Asbridge 2012, pp. 104–06
- Asbridge 2012, p. 106
- Asbridge 2012, pp. 111–13
- Asbridge 2012, p. 114
- Lock 2006, pp. 144–45
- Lock 2006, pp. 146–47
- Jotischky 2004, p. 85
- Asbridge 2012, pp. 201–18
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