Bala Hissar is an ancient fortress located in the city of Kabul, Afghanistan. The estimated date of construction is around the 5th century A.D. 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.