At the beginning of the period 1000 to 1400, the Umayyad caliphate collapses, fragmenting Islamic power in the Iberian Peninsula. Christian kingdoms in the north gradually unite, become much more powerful, and expand their territories through a campaign of reconquista (reconquest). Despite the weakening of Islamic power, its influence in science, medicine, and art is extraordinary and contributes to the rich diversity of the peninsula as Christians, Muslims, and Jews live peacefully together. By the end of the period, the Christian kings conquer virtually all of Muslim al-Andalus, leaving Granada and the surrounding territory as the last bastion of Islamic Iberia.