When Sultan Mehmed II succeeded his father in 1451 , he was just nineteen years old . Many European courts assumed that the young Ottoman ruler would not seriously challenge Christian hegemony in the Balkans and the Aegean . This calculation was boosted by Mehmed 's friendly overtures to the European envoys at his new court . But Mehmed 's mild words were not matched by actions . By early 1452 , work began on the construction of a second fortress ( '' Rumeli hisarı '' ) on the Bosphorus , on the European side several miles north of Constantinople , set directly across the strait on the Asian side from the '' Anadolu Hisarı '' fortress , built by his great-grandfather Bayezid I . This pair of fortresses ensured complete control of sea traffic on the Bosphorus ; and defended against attack by the Genoese colonies on the Black Sea coast to the north . ( This new fortress , was called '' Boğazkesen '' , which means ' strait-blocker ' or ' throat-cutter ' , to emphasize its strategic position . ) In October 1452 , Mehmed ordered Turakhan Beg to station a large garrison force in the Peloponnese to block Thomas and Demetrios ( despotes in Southern Greece ) from providing aid to their brother Constantine XI Palaiologos during the impending siege of Constantinople . Michael Critobulus says about the speech of Mehmed II to his soldiers : " My friends and men of my empire ! You all know very well that our forefathers secured this kingdom that we now hold at the cost of many struggles and very great dangers and that , having passed it along in succession from their fathers , from father to son , they handed it down to me . For some of the oldest of you were sharers in many of the exploits carried through by them — those at least of you who are of maturer years — and the younger of you have heard of these deeds from your fathers . They are not such very ancient events nor of such a sort as to be forgotten through the lapse of time . Still , the eyewitness of those who have seen testifies better than does the hearing of deeds that happened but yesterday or the day before . " Byzantine Emperor Constantine XI swiftly understood Mehmed 's true intentions and turned to Western Europe for help ; but now the price of centuries of war and enmity between the eastern and western churches had to be paid . Since the mutual excommunications of 1054 , the pope in Rome was committed to establishing authority over the eastern church . Nominal union had been negotiated in 1274 , at the Second Council of Lyon , and indeed , some Palaiologoi emperors ( Latin , Palaeologan ) had since been received into the Latin Church . Emperor John VIII Palaiologos had also recently negotiated union with Pope Eugene IV , with the Council of Florence of 1439 proclaiming a '' Bull of Union '' . These events , however , stimulated a propaganda initiative by anti-unionist Orthodox partisans in Constantinople ; the population , as well as the laity and leadership of the Byzantine Church , became bitterly divided . Latent ethnic hatred between Greeks and Italians , stemming from the events of the Massacre of the Latins in 1182 by the Greeks and the sack of Constantinople in 1204 by the Latins , played a significant role . Finally , the attempted Union failed , greatly annoying Pope Nicholas V and the hierarchy of the Roman church
Massacre of the Latins
Massacre of the Latins
Fall of Constantinople