The County of Barcelona was originally a frontier region under the rule of the Carolingian dynasty. By the end of the 10th century, the Counts of Barcelona were de facto independent, hereditary rulers in constant warfare with the Islamic caliphate of Córdoba and its successor states. The counts, through marriage alliances and treaties, acquired the other Catalan counties and extended their influence along Occitania. Barcelona formed then nucleus of the emergent Principality of Catalonia. In 1164, the count of Barcelona, Alfons I, inherited the Kingdom of Aragon (as Alfonso II). Thenceforward, the history of the county of Barcelona is subsumed within that of the Crown of Aragon, but the city of Barcelona remained preeminent within it.