The Ottomans were not the first Islamic power to threaten the Byzantine Empire, and in fact the empire was by this point in 1453 a hollowed out husk of its former glory. Successive waves of Turkish and Mongol invasions had taken almost all of Anatolia out of Byzantine control, and the Ottomans had by this point conquered considerable portions of the empire’s Balkan territories. Constantinople itself, whose population may once have been as high as 800,000 people (500,000 is more realistic), never recovered from the Fourth Crusade’s sacking and the Black Death, and probably only had housed about 50,000 by the mid 15th century. But the city had survived several sieges by Islamic armies (including the Ottomans) in the past, because of its seemingly impenetrable walls. Unfortunately for the Byzantines, this time the Ottomans came packing some of the strongest cannons yet invented.