After capturing Ctesiphon, several detachments were immediately sent west to capture Qarqeesia and Heet, forts at the border of Byzantine empire. Strong Persian garrisons north-east of Ctesiphon at Jalula and north of Tigris at Tikrit and Mosul, posed a threat to Muslim invaders. The greatest threat of all was the Persian concentration at strategic fort of Jalula.

The Persian forces at Jalula were commanded by general Mihran Razi. His deputy was General Farrukhzad a brother of General Rostam Farrokhzād, who commanded Persian forced at Battle of Qadisiyyah.

Jalula was a town of great strategic importance, a bottle-neck to Northern Iraq. To have Jalula under the rule meant to have the gate to Northern Iraq. Persians therefore expected an attack on Jalula. Defense of Jalula was also very important for the strength of Empire and maintain order in the far flung frontiers of the Persian Empire.

As instructed by the Caliph Umar, Saad ibn Abi Waqqas, Muslim commander in chief on the Persian front, reported all the strategic situation to Umar who decided to deal with Jalula first. His plan was to first clear his rear before any decisive action further north against Tikrit and Mosul. Umar appointed Hashim ibn Utba to the expedition of Jalula. Some time in April 637, Hashim marched at the head of 12,000 troops from Ctesiphon and made contact with Persians outside Jalula fort.^[2]

At Jalula, both the flanks of Persians and Muslims rested upon natural obstacles. Diyala River on east and broken ground on the west. Broken ground was unsuitable for cavalry and even the movement of infantry en masse was difficult and would have exposed them to Persian Fire-Power.

Mihran, the Persian commander at Jalula, was a veteran general who had fought Muslims in Qadisiya and knew well of the Muslims' tactics. He dug entrenchments and placed caltrops in front of them, to slow down Muslim advances. The Persian troops intended to wear the Muslims down by letting them launch a frontal attack thus exposing themselves to Persian archers and siege engines led artillery. The caltrops also hindered the speed of Muslim cavalry and infantry. Mihran deployed his army in classical defensive formation with the intention of launching the attack when Muslims had suffered enough and the nucleus of their power had been destroyed.

Hashim, the Muslim commander, on reaching the battlefield, analyzed that the Persians could not be attacked from the flanks due to those natural barriers and approaching them from the front would be costly. He decided to lure the Persians out of the defenses of entrenchments and caltrops. Hashim planned to launch a frontal attack and make a feint retreat under Persian fire, and once the Persians were away from their trench, his cavalry would capture the bridge on the trench, cutting off the Persians' escape route.

Rashidun troops deployment edit

In the records of Muslim chroniclers from the era of the 7th century to 10–11th centuries there is known the detail about the composition of the Rashidun army and units involved in this battle. There is some version of the deployment composition.

It is recorded by Tabari that the Rashidun army was composed of 12,000 troops with the deployment as follow:

• Hashim ibn Utba as overall commander
• Al-Qa'qa'a ibn Amr at-Tamimi commanding the vanguard
• Si'r bin Malik commanding the right wing of the army.
• Amr bin Malik bin Utba commanding the left wing of the army.
• Amr bin murra al Juhani commanding the rear guards.

While Talha (Tulayha) ibn Khuwaylid ibn Nawfal al-Asadi; Amru bin Ma'adi Yakrib; Qays ibn Makshuh and Hujur bin Adi were coming later as the reinforcements. Generally, the overall troops were consisting of prominent figures of the Ansar and Muhajireen during the first battles of Muslims and portions of Bedouin who formerly rebelled during Ridda wars^[3]

Ahmad ibn A'tham provides a slightly different version from Tabari's composition, namely:

• Jarir bin Abdullah al Bajali commanding the right wing of the army.
• Hujr bin Abdullah al-Kindi commanding the left wing of the army.
• Makshuh al Muradi commanding the obscure placement of wing units of the army.
• Amr bin murra al Juhani commanding the cavalry in the center.
• Talha (Tulayha) ibn Khuwaylid ibn Nawfal al-Asadi commanding the infantry.^[3]

Baladhuri also mentions very briefly a composition which is similar to that of Ahmad ibn A'tham's, except he includes Jarir bin Abdullah.^[3]

The battle began with Muslim's frontal attack; after engaging for some time Muslims feint a retreat and fell back in an organized manner. Mihran, sensing the time is on hand to launch an offensive for him, ordered the entrenchments to be bridged. Once the Persian army had attained the battle formation he ordered a general attack. Up till now the battle had progressed as both commanders had planned. Once Mihran engaged his troops in an open battlefield, Hashim decided to carry out his manoeuvre. He dispatched a strong cavalry regiment under one of his most illustrious cavalry commanders; Qaqa ibn Amr, to capture the bridge over the entrenchments. The bridge was not heavily guarded as virtually all the Persian troops available were used to assault Muslim's main body. Qaqa manoeuvred around Persian right flank and quickly captured the bridge at their rear. The news of a strong Muslim cavalry detachment in their rear was a serious setback to Persian morale. Hashim launched a frontal attack with Muslim infantry while Qaqa stuck at Persian rear with his cavalry. Persian troops were trapped between the Muslim army and the natural barriers on the battlefield. Nevertheless, thousands of them managed to escape and reached the Jalula fortress.

•  
  The Muslims' feint retreat
•  
  Persian offensive
•  
  General engagement
•  
  Qaqa's outflanking maneuver

The Persians suffered heavy casualties and the battle ended in a complete Muslim victory. Women and Children were enslaved as Spoils of war and Umar says « in fear of Children of these Slave-women who are going to be born, I seek refuge in Allah».^[4] After the battle Hashim laid siege to Jalula. Persian emperor Yazdegerd III was in no position to set a relief force to Jalula and the fortress surrendered to Muslims seven months later on the terms of annual payment of Jizya (tribute). After capturing Jalula Muslims captured Tikrit and Mosul, completing their conquest of Iraq.

After the conquest of Iraq (region west of Zagros mountains) Umar decided to consolidate the conquered territory. He, apparently for the time being, did not want further conquest. He was almost on the defensive until the consistent Persian raids in Iraq compelled him to launch a large scale invasion of the Persian empire.

• Islamic conquest of Persia
• Muslim conquests
• Sassanid Empire

34°17′00″N 45°10′00″E / 34.2833°N 45.1667°E / 34.2833; 45.1667