Great Wall of Gorgan

The Great Wall of Gorgan is a series of ancient defensive fortifications located near Gorgan in the Golestān Province of northeastern Iran, at the southeastern part of the Caspian Sea. 37°04′13″N 54°04′36″E / 37.070382°N 54.076552°E / 37.070382; 54.076552

The wall is located at a geographic narrowing between the Caspian Sea and the mountains of northeastern Iran, 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, and the wall is believed to have protected the Sassanian Empire to the south from the peoples to the north. It is 195 kilometres long and 6 to 10 metres wide, and features over 30 fortresses spaced at intervals of between 10 and 50 kilometres. It is surpassed only by the Great Wall of China as the longest defensive wall in existence.

It is also known as The Red Snake among archaeologists due to the colour of its bricks, and as the Gorgan Defence Wall, Anushirvân Barrier, Firuz Barrier and Qazal Al'an, Sadd-i-Iskandar (Persian for dam or barrier of Alexander), as Alexander the Great is said to have passed through the Caspian Gates on his hasty march to Hyrcania and the east.