 The Christian realms of León, Navarre and Catalonia lacked a common identity and shared history based on tribe or ethnicity so they frequently united and divided during the 11th and 12th centuries.Although small, all developed an aristocratic military technique and in 1031 the disintegration of the Caliphate of Córdoba in southern Spain created the opportunity for the territorial gains that later became known as the Reconquista.In 1063 William VIII of Aquitaine led a combined force of French, Aragonese and Catalan knights to take the city of Barbastro that had been in Muslim hands since the year 711.