Great Wall of Gorgan

The Great Wall of Gorgan is a Sasanian-era defense system located near modern Gorgan in the Golestān Province of northeastern Iran, at the southeastern corner of the Caspian Sea. The western, Caspian Sea, end of the wall is near the remains of the fort at: 37.13981°N 54.1788733°E / 37.13981; 54.1788733; the eastern end of the wall, near the town of Pishkamar, is near the remains of the fort at: 37.5206739°N 55.5770498°E / 37.5206739; 55.5770498. The title coordinate is for the location of the remains of a fort midway along the wall.

The wall is located at a geographic narrowing between the Caspian Sea and the mountains of northeastern Iran. It is one of several Caspian Gates at the eastern part of a region known in antiquity as Hyrcania, on the nomadic route from the northern steppes to the Iranian heartland.

Source: Wikipedia