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 a staggering 20 feet (6.1 m) high and 12 feet thick, start at the fortress and follow the mountain ridge in a sweeping curve down to the river. It sports a massive set of gates for access to the fortress.Bala Hissar was originally divided into two parts.The lower fortress, containing the stables, barracks and three royal palaces and the upper fortress housing the armory and the dungeon of Kabul, known as the infamous Black Pit.