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 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. The wall is described as "amongst the most ambitious and sophisticated frontier walls" ever built in the world and the most important of the Sasanian defense fortifications. 1 mi). It is surpassed only by the wall systems of the Great Wall of China and Cheolli Jangseong (in modern-day North Korea) as the longest single-segment building and the longest defensive wall in existence.