Also known as the “Red Snake” for its distinctive red-colored bricks, the “Great Wall of Gorgon” was a 121-mile rampart that extended from the southern coast of the Caspian Sea to the Elburz Mountains in what is now Iran.
It was once thought to have been the work of Alexander the Great—it was even known as “Alexander’s Barrier”—but more recent research suggests it was built by the Sasanian Persians sometime around the 5th century A.D.
When completed, it was one of the longest walls of antiquity and boasted more than 30 forts, a garrison of 30,000 troops and a network of canals that acted as both a water supply system and a defensive moat. Surprisingly little is known about the wall’s history, but most scholars believe the Persians used it to guard against the Hephthalite Huns and other enemies to the north.