In 910 much of the Iberian peninsula was governed by Muslims from the Maghreb (Moors) and was known as al-Andalus. The Muslim occupation of parts of the Iberia peninsula dates to the Umayyad victory over the Visigoths in 711. Al-Andalus was ruled by the emirs of Cordova, whose control over the region – in particular the borders with the Christian kingdoms to the north – fluctuated according to the fortunes of individual emirs. This period was the golden age of al-Andalus: the city of Cordova, with a population of half a million, was a magnetic cultural centre, replete with famous libraries and universities that drew scholars from all over Medieval Europe; advanced irrigation agriculture, supplemented by imports from the Middle East, ensured a flourishing and stable economy. Following the initial Moorish conquest in the 8th century, embattled Christians had retreated to the northern regions and had been assisted by the Franks in holding back the Moorish advance. A shifting mosaic of feudal counties and nascent kingdoms was emerging in the shadow of the Pyrenees and resisting, and sometimes succumbing to, incursions from the Emirate of Cordova. Charlemagne had established the vassal frontier march of Barcelona (Catalonia) in the 9th century. The Christian Kingdom of Asturias, established after the Umayyad conquest in the 8th century, gave way to the Kingdom of Léon when the Asturian king Alfonso the Great divided his kingdom between his three sons and Léon was inherited by Garcia I (r. 910–914). In the early 10th century Castile was emerging as a frontier lordship of the kingdom of León and Navarre had been proclaimed a kingdom by the Basque leader Sancho Garcés (905–25).