Córdoba, the capital of the caliphate since Abd-ar-Rahman III, was the largest, richest and most sophisticated city in western Europe. Mediterranean trade and cultural exchange flourished. Muslims imported a rich intellectual tradition from the Middle East and North Africa. Some important philosophers at the time were Averroes, Ibn Arabi and Maimonides. The Romanised cultures of the Iberian Peninsula interacted with Muslim and Jewish cultures in complex ways, giving the region a distinctive culture. Outside the cities, where the vast majority lived, the land ownership system from Roman times remained largely intact as Muslim leaders rarely dispossessed landowners and the introduction of new crops and techniques led to an expansion of agriculture introducing new produces which originally came from Asia or the former territories of the Roman Empire.