The city of Zaragoza was founded by the Roman emperor Augustus. Visigoths conquered the area in the late 5th cent. and Muslims in the early 8th cent. Carolingians pushed out the Muslims (c.850), and Aragón came under the rule of Navarre. At the death (1035) of Sancho III of Navarre, his western territories were organized as the kingdom of Aragón for his illegitimate son, Ramiro I. He and his successors, notably Alfonso I, extended their dominions southward at the expense of the Moorish emirate of Zaragoza, and in the 12th cent. Zaragoza replaced Huesca as the capital.

In 1076, Aragón annexed Navarre, and in 1137 it became united, through personal union, with Catalonia. Both regions preserved their own Cortes, laws, languages, and customs and evolved along separate lines; their deep historical, social, and cultural differences at times caused great friction. With the expansion of the house of Aragón (see separate article), the name Aragón came to signify a confederation of its Spanish possessions (Aragón, Catalonia, Majorca, and Valencia) and several French fiefs. In the bitter struggles (12th–15th cent.) between kings and nobles, the nobles gained more and more privileges until Peter IV defeated them in 1348. The justiciar, a type of magistrate created in the 12th cent., acted as a sort of intermediary between king and nobles; after 1348 he lost most of his political power but gained more juridical importance. Aragón played only a minor role in the expansionist policy of its kings in the Mediterranean.

United with Castile after 1479 through the marriage of Ferdinand V (Ferdinand the Catholic) with Isabella, Aragón preserved its cortes and its city privileges. These, however, were gradually limited by the centralizing policies of the Spanish monarchy, and in 1716 Philip V abolished most of the remaining political privileges to punish the Aragonese for siding with Archduke Charles (later Emperor Charles VI) in the War of the Spanish Succession. The passionate attachment of the Aragonese to their liberties was illustrated by the episode of Antonio Pérez under Philip II and by the heroic defense of Zaragoza in the Peninsular War. In 1833 the administrative unit of Aragón was divided into the three present provinces. The provinces became an autonomous region in 1981.