Badajoz was founded by Abd-al Rahman Ibn Marwan in 875. After he had led several rebellions, he was expelled by Mérida but was given the chance to found a new city. Here, on a hill commanding the new city, he built a large citadel which granted Badajoz a strategic role in controlling the passage from Portugal to central Iberia.

The current line of walls date mostly from the Almohad age, although there are traces of earlier work from 913 and 1030; in 1169 the Almohad caliph Abu Yaqub Yusuf rebuilt the fortress, giving it its current appearance. The last Muslim restoration was carried on by Abu Yahya ibn Abi Sinan in the 13th century, few years before the capture of the city by the Christian King Alfonso IX of León.

During the Peninsular War (1805-1813) the citadel was successfully stormed by allied-British, Spanish & Portuguese forces under the command of the Duke of Wellington. As a result, the Napoleonic hold on Western Spain was significantly weakened, and the Storming of the Alcazaba became part of Wellington's growing reputation for success in battle.

The citadel measures 400 by 200 metres (1,310 ft × 660 ft). It is bounded to the north by the Guadiana river and to the east by the Rivillas torrent. The less steep parts of the slopes and other strategically weak points are defended by towers. The whole line of walls features a parapet, while the barbican and the ditch which once added protection have disappeared.

In the towers area was the palace of the lords of Badajoz, featuring several baths and mosques. After the Christian conquest, the largest, the Great Mosque, was turned into a church, Santa María de Calatrava, which acted as the cathedral of Badajoz until the construction of the current one. The Great Mosque had five naves separated by arches supported by columns, and external buttresses. For its construction elements of Roman and Visigoth edifices were used, such as capitals and columns. Another building of the Muslim palace which was converted after the Christian conquest was the Military Hospital, now home to the Library of Extremadura.

Another building in the Alzacaba is the Palace of the Dukes of Feria, built by the Grand Master of the Order of Santiago, Lorenzo Suárez de Figeroa (1387–1410). Built in Renaissance style with Mudéjar elements, it was restored in the 17th century. The façade features a central arch connecting two square towers with irregularly place windows; the palace has a trapezoidal plan and a cloister. It is currently home to the Provincial Archaeological Museum.

Among the towers, the most significant is the Espantaperros Tower (Spanish: Torre de Espantaperros or Torre de la Atalaya), built in 1169 and with a height of 30 metres (98 ft). It has an octagonal plan, and is surmounted by a small temple added in Mudéjar style in the 16th century.

Other towers include:

• Torre de las Siete Ventanas
• Torre de las Doncellas
• Torre del Alpéndiz
• Torre Abarlongada
• Torre de la Horca or Torre de los Ahorcados
• Torre de Santa María, the most visible remain of the ancient cathedral
• Torre del Palacio Episcopal (Bishop's Palace Tower)

Gates include:

• Puerta del Capitel, one of the two original Almohad gates which have been preserved
• Puerta de Yelves o de Carros
• Puerta del Alpéndiz, in the northern side of the citadel
• Puerta de la Coraxa or Puerta de la Traición

The Alcazaba includes also a large park.

• Taifa of Badajoz
• Badajoz bastioned enclosure

• Page at Badajoz's municipal website (in Spanish and Portuguese)