The County of Barcelona was a polity in northeastern Iberian Peninsula, originally located in the southern frontier region of the Carolingian Empire. In the 10th century, the counts of Barcelona progressively achieved independence from Frankish rule, becoming hereditary rulers in constant warfare with the Islamic Caliphate of Córdoba and its successor states. The counts, through marriage, alliances and treaties, acquired or vassalized the other Catalan counties and extended their influence over Occitania. In 1162, the County of Barcelona entered into a personal union with the Kingdom of Aragon. Thenceforward, the history of the county is subsumed within that of the Crown of Aragon, but the city of Barcelona remained preeminent within it.