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 peoples to the north, probably the White Huns. In his 2014 book Empires and Walls, sociologist Mohammad A. Chaichian questions the validity of this interpretation using historical evidence of potential political-military threats in the region as well as the economic geography of the Gorgan Wall's environs. 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.

It is 195 km (121 mi) long and 6–10 m (20–33 ft) wide and features over 30 fortresses spaced at intervals of between 10 and 50 km (6.2 and 31.1 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.