By the time Mehmed became Sultan Mehmed II of the Ottoman Empire (1451), the Byzantine Empire was reduced to Constantinople itself, the Peloponnese, and a handful of Aegean islands. The Ottomans had had control of the territory surrounding Constantinople for decades. Mehmed fortified both sides of the Golden Horn, and would eventually lay siege to Constantinople.
Those fortifications were largely there to block reinforcements from the Black Sea, namely the Genoese in the area. In response, the Byzantines stretched a chain across the Golden Horn to keep the Ottomans from using their naval superiority to assault a section of the walls.
Some Christian reinforcements managed to get past the blockade, and Mehmed decided to make up for his navy’s failures by rolling his ships on greased logs overland, then putting them back in the water behind the chain. This rendered the Byzantines chain useless, spread their troops to defend all of the city’s walls, and made the siege much easier on the Ottomans.
