The Great Wall of Gorgan, also called the Gorgan Defence Wall, Anooshirvan Barrier, Firooz Barrier and sometimes Alexander Dam is an ancient defensive facility located in the Gorgan region of northeastern Iran. It is also known as The Red Snake among archaeologists due to the color of its bricks. It protects the Caspian Gates which in turn gave access for the nomads of the northern steppes to the Iranian heartland, and through which Alexander passed on his hasty march to Hyrcania and the east. The wall is second only to the Great Wall of China as the longest defensive wall in existence, but over a thousand years older and of more solid construction than the present form of the Great Wall.
The barrier consists of a wall, 195 kilometers long and 6 to 10 meters wide, along the length of which are located a number of fortresses, spaced at intervals of between 10 and 50 kilometers. The 40 identified castles vary in dimension and shape but the majority are square fortresses, made of the same brickwork as the wall itself and at the same period. The wall is made of standardized bricks, made from the local loess soil, and fired in kilns along the line of the wall. This wall starts from the Caspian coast, circles north of Gonbad’e Kavoos, continues towards the northwest, and vanishes behind the Pishkamar Mountains.
If one assumes that the forts were occupied as densely as those on Hadrian's Wall, then the garrison on the Gorgan Wall would have been in the order of 30,000 men. Models, taking into account the size and room number of the barrack blocks in the Gorgan Wall forts and likely occupation density, produce figures between 15,000 and 36,000 soldiers. Even the lowest estimate suggests a strong and powerful army.
Dr. Kiani who led an archaeological team in 1971 believed that the wall was built during the Parthian dynasty (to protect mainland Iran from invasion from the north) simultaneously with the construction of the Great Wall of China and it was restored during the Sassanid era (3-7th c. A.D.). In 2005 a team excavated samples of charcoal from the many brick kilns along the wall, and samples from the Gorgan Wall and the smaller Wall of Tammishe; OSL and radiocarbon dating indicated a date for both walls in the late 5th or 6th century CE.
In 2006, based on a decision by members of Cultural Committee of the High Council for Cultural Heritage of the Iranian Cultural Heritage and Tourism Organization (ICHTO), information on this historic wall will be compiled in a single file to be submitted to UNESCO for registration in its temporary list as the first step toward its world registration.