The Zindan Gate was built in the middle of the 15th century for better protection of the East Gate, which at the time was the main entrance to the city. The gate is actually a small pre-fortification — a barbican consisting of two massive semicircular towers, between which there is a passage. Above the arch of the gate there was a small rectangular niche with a place for the icon of the protector of the city. There were seven cannon openings on the towers and the arched rampart of this complex. This was the place where the artillery defence system was applied for the first time, that is, a defence with firearms. It was from these positions that Belgrade successfully resisted the Turkish sieges in 1456 and 1521.