The fall of Constantinople in 1453 (only 3 years before the Ottoman siege at Belgrade) sent panic and fear throughout Europe and the Christian world. The loss of Constantinople was regarded as a calamitous setback for Christian Europe and the crusades. The victorious Sultan Mehmet II, encouraged by his momentous victory at Constantinople, began an advance into the Balkans and northward in the hopes of defeating Hungary and reaching Western Europe. Mehmed II would take Serbia in 1454-55; and the following year with an army estimated to be 70,000 strong (other historians have estimated that Mehmed’s army may have been between 100,000-300,000 men), he launched what would be a long and arduous march to Belgrade.
Belgrade (Nándorfehérvár) was a key stronghold of the southern defense system of medieval Hungary. The epic battle between the Ottoman Empire and Hungary would come to significantly influence the subsequent history of Europe and the spread of Ottoman domination in the Balkans. János (John) Hunyadi, an influential and famous Hungarian military commander, politician and noble, took the responsibility for coordinating and controlling the defensive operations along the southern borders of Hungary (a position he was appointed to in 1441). Hunyadi, knowing of the Ottoman advance in the Balkans, left 7,000 of his soldiers in Belgrade to build and strengthen its defensive capabilities in May of 1456. In the buildup to the Ottoman siege, John of Capistrano, a Franciscan monk appointed by the pope to recruit as many troops as it was possible, crisscrossed the Kingdom of Hungary and Western European powers to raise a volunteer force. By June, 1456 Capistrano’s army and the Hungarian forces (numbering approximately 45,000-50,000 in total) arrived in Belgrade and began to take up their defensive positions north of the city.
