On the Iberian Peninsula there was no significant Christian polity. 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. This had the full support of Alexander II, and a truce was declared in Catalonia with indulgences granted to the participants. It was a holy war but differed from the First Crusade in that there was no pilgrimage, no vow, and no formal authorisation by the church. Shortly before the First Crusade, Urban II had encouraged the Iberian Christians to take Tarragona, using much of the same symbolism and rhetoric that was later used to preach the crusade to the people of Europe.