The siege of Belgrade, or siege of Nándorfehérvár was a military blockade of Belgrade that occurred 4–22 July 1456 in the aftermath of the fall of Constantinople in 1453 marking the Ottomans' attempts to expand further into Europe. Led by Sultan Mehmed II, the Ottoman forces sought to capture the strategic city of Belgrade, which was then under Hungarian control and was crucial for maintaining control over the Danube River and the Balkans.