The Alcazaba of Badajoz is a Muslim fortification (9th-13th centuries), a late medieval Christian castle (13th-16th centuries) and part of the citadel and modern fortification (17th-19th centuries).

The citadel-castle of Badajoz is the largest citadel-castle in Europe and one of the largest of its kind and period in the world in terms of its perimeter (8 hectares and some 1,300 metres of preserved wall), However, it became much larger with the so-called 'Old Fence' (of which important traces still survive), which comprises approximately the whole of the later-built bastioned enclosure, measuring 6,000 metres and covering more than 50 hectares, making it the largest of all those built by the Arabs in the past.

The city of Batalyaws, modern-day Badajoz, was founded by Abd-al Rahman Ibn Marwan in 875, during the reign of the Cordovan Amir Muhammad I, over an earlier Visigothic settlement.

After leading several rebellions, Ibn Marwan was unable to return to his place of residence (Mérida), although he was allowed to found a new city; he asked the amir to build the city on the present-day Cerro de San Cristóbal, but he was not allowed to build anywhere else but on the "Cerro de las Muelas", on the left bank of the Guadiana River.

The site chosen to erect the Alcazaba (originally made of mortar), and to found the city, was finally Cerro de la Muela. Since its foundation, and due to its strategic location on the border with Portugal, the city has had a marked character of a stronghold.

The walled enclosure comes mostly from the Almohad period, although there are remains from earlier periods and witnesses of later restorations. The first restoration was carried out with rammed earth by 'Abd Allah ibn Muhammad ibn 'Abd al-Rahmann, grandson of Ibn Marwan, in the year 913.

The walls of the Alcazaba have survived to the present day in practically the same form as they were originally in the Almohad period. The area near El Metido (which faces the side of the Arroyo Rivillas) underwent reconstruction in the 19th century due to the heavy siege suffered during the war.