By the beginning of the fifteenth century, many had concluded that Constantinople was unable to survive as an independent city. The city had already fallen to Crusaders in 1204, and was no longer regarded as invincible – despite its formidable system of defenses. By the late fifteenth century, Islamic leadership was in the process of passing from the Abbasid Caliphate to the Ottomans, who regarded the conquest of Christendom’s greatest city as a jihad – a holy war. The expansionist policies of the Ottoman Turks led to the city being surrounded, and deprived of any economic or political hinterland. The “Second Rome” was isolated. It had earlier been fatally weakened through a natural disaster. Between 1348–50, the “Black Death” spread within the city, killing as much as half the population. It was just a matter of time before the city fell.
The Ottoman sultan Mehmed II constructed a fortress in Ottoman territory just north of Constantinople in 1452, which served the dual purpose of cutting off the city’s links with Black Sea ports on the one hand, and acting as the launching point for the siege of Constantinople a year later on the other. Mehmed II laid siege to Constanti- nople in April and May 1453. After fifty-seven days, the city fell. Strained relations between the Christian west and east led to a marked absence of support, political or military, for the besieged city. Having secured the city, Mehmed continued to expand Ottoman influ- ence in the region now known as the Balkans.