The Caliphate of the Ottoman Empire (Ottoman Turkish: خلافت مقامى, romanized: hilâfet makamı, lit. 'office of the caliphate') was the claim of the heads of the Turkish Ottoman dynasty to be the caliphs of Islam in the late medieval and the early modern era. During the period of Ottoman expansion, Ottoman rulers claimed caliphal authority after the conquest of Mamluk Egypt by Sultan Selim I in 1517, which bestowed the title of Defender of the Holy Cities of Mecca and Medina upon him and strengthened the Ottoman claim to caliphate in the Muslim world.