Kalat-i-nadiri

Kalat-i-nadiri is a massive natural fortress located about 44 miles north of Sousia in the Kalat, Khorasan region of 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.

References

Engels, Donald W. "Alexander the Great and the Logistics of the Macedonian Army", University of California Press. 1978. Pages 87, 88.