In 1453, after a siege of some weeks, the Ottoman sultan Mehmed II captured Constantinople, ending the Byzantine Empire and making the city the new Ottoman capital, later known as Istanbul. The conquerors converted the cathedral of Hagia Sophia into a mosque and reorganised the city around great imperial mosque complexes (külliye) that bundled mosque, school, hospital and market under religious endowments. Bazaars such as the Grand Bazaar and a repopulation policy revived the depleted city. The conquest was aided by large cannon that breached the famous land walls.
It showed how a captured city is comprehensively re-planned to express a new religious and political order. The külliye-based reorganisation became a defining model of Ottoman urban form across the empire.