The Aljafería began outside medieval Zaragoza as the eleventh-century pleasure palace of Abū Jaʻfar Aḥmad al-Muqtadir, ruler of the taifa kingdom of Saraqusta. Built during a period of political fragmentation and intense artistic exchange in al-Andalus, it combined fortified walls and towers with gardens, courtyards, reception halls, private apartments, and a small mosque. Interlacing arches, carved stucco, inscriptions, painted surfaces, and geometric ornament created a ceremonial setting in which the ruler displayed learning, wealth, and legitimacy. The palace was known as the Palace of Joy.

Alfonso I of Aragon conquered Zaragoza in 1118, and the palace became a residence of Christian monarchs. Rather than simply erase Islamic work, successive rulers reused and altered it. Peter IV added a Gothic-Mudéjar palace in the fourteenth century, employing craftspeople whose timber ceilings, brickwork, and ornament drew on Islamic traditions under Christian patronage. Ferdinand and Isabella commissioned another royal suite in the late fifteenth century, including a grand staircase and richly decorated ceilings. These additions turned the complex into a physical record of changing dynasties, religions, languages, and artistic techniques.

The Aljafería also housed institutions of coercive power. The Spanish Inquisition used parts of it, and Philip II surrounded the palace with a Renaissance-style citadel after unrest in Aragon. Military conversion intensified during later centuries as barracks, offices, and utilitarian partitions replaced or concealed palace spaces. Damage, neglect, and insensitive alteration stripped decoration and changed walls. Nineteenth-century scholars protested the losses, but the army continued to occupy the complex. By the twentieth century, important Taifa and Mudéjar elements survived amid extensive later construction and areas whose original appearance was uncertain.

Large restoration campaigns began in the mid-twentieth century and continued for decades. Conservators exposed archaeological remains, removed some barracks fabric, reset fragments, reconstructed arcades and wall surfaces, and used casts or modern plaster to restore legibility. Original ornament is often distinguishable from smoother replacement work, but the palace visitors see is substantially shaped by modern interpretation. Adaptation in the 1980s made the Aljafería the seat of the Cortes of Aragon. New parliamentary spaces and services were inserted while monumental rooms underwent further conservation. UNESCO recognizes its Mudéjar components within the Architecture of Aragon listing.

The regional parliament occupies and helps steward the palace, and public visits are ticketed and may vary with legislative activity, security, exhibitions, or conservation. The Aljafería is neither an untouched Islamic palace nor a wholesale replica. It contains important eleventh-century structures and fragments, medieval Christian additions, early modern fortification, later military layers, and extensive twentieth-century reconstruction. Its significance lies precisely in that complex survival. Responsible viewing distinguishes original carved surfaces from restored patterns and treats Islamic, Jewish, and Christian histories as intertwined parts of Aragon's past rather than a simple sequence of conquest and replacement.