Meanwhile, the Ottoman issue had again become acute, and, after the fall of Constantinople in 1453, Sultan Mehmed II was rallying his resources to subjugate Hungary. His immediate objective was Nándorfehérvár (today Belgrade). Nándorfehérvár was a major castle-fortress, and a gatekeeper of south Hungary. The fall of this stronghold would have opened a clear way to the heart of Central Europe. Hunyadi arrived at the Siege of Belgrade at the end of 1455, after settling differences with his domestic enemies. At his own expense, he restocked the supplies and arms of the fortress, leaving a strong garrison there under the command of his brother-in-law Mihály Szilágyi and his own eldest son László Hunyadi. He proceeded to form a relief army, and assembled a fleet of two hundred ships. His main ally was the Franciscan friar, Giovanni da Capistrano, whose fiery oratory drew a large crusade made up mostly of peasants. Although relatively ill-armed (most were armed with farm equipment, such as scythes and pitchforks) they flocked to Hunyadi and his small corps of seasoned mercenaries and cavalry.