The Herat Citadel, also known as the Citadel of Alexander or the Citadel of Herat, is an ancient fortress located in the city of Herat, Afghanistan. The citadel dates back to the 3rd century BC and has served as an important center of power and commerce throughout the centuries.

The Herat Citadel is believed to have been built by Alexander the Great during his conquest of the region in the 3rd century BC. It was later used by the Timurids, the Safavids, and the Mughals, among others, as a military base and administrative center.

The citadel is a massive structure, with walls that are up to 15 meters high and over 3 meters thick. It is built of baked bricks, with towers and bastions at each corner. The citadel is surrounded by a moat that is 15 meters wide and 10 meters deep, which served as a defensive barrier against invading armies.