Great Wall of Gorgan — Wikipedia

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 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 Eurasian Steppe to the Iranian heartland. The wall is believed to have protected the Sasanian Empire to the south from the foreign peoples of the north, probably the White Huns....