After the Ottoman conquest of Egypt in 923 / 1517, the local rulers of Mecca offered Sultan Selim I supreme power over Arabia for political and economic reasons. Consequently, the two most important Muslim cities, Mecca and Medina – and with them the holiest places of Islam – became part of the Ottoman Empire, and the sultans took the title of Caliph. Thus, for about 400 years the Ottoman sultans paid particular attention to giving their generous support to the holy sites.