Kalat-e Naderi (Persian: کلات نادری) is a massive natural fortress located about 44 miles north of Sousia, in Kalat County, Razavi Khorasan Province, Iran.
It is essentially a massive plateau about 4 miles in circumference that has been used as a fortress since before the Achaemenid era. It is surrounded on 3 sides by high cliff walls ranging from 1500 feet on the south side to 2000 feet on the west side with lower eastern walls and a gently sloping plain leading up to the heights from the north.
It is famous as the only fortress ever to withstand a siege by Tamerlane.
Alexander the Great's army laid siege to it. While Alexander left to deal with a rebellious Persian chieftain, he ordered Craterus to command the majority of the army and take the fortress.