Bala Hissar ("High Fort") is an ancient fortress located in the south of the old city of Kabul, Afghanistan. The estimated date of construction is around the 5th century AD. Bala Hissar sits to the south of the modern city centre at the tail end of the Kuh-e-Sherdarwaza Mountain. The Walls of Kabul, which are 20 feet (6.1 m) high and 12 feet (3.7 m) thick, start at the fortress and follow the mountain ridge in a sweeping curve down to the river. It sports a set of gates for access to the fortress. The Kōh-e Shēr Darwāzah (lion door) mountain is behind the fort.