Great Wall of Gorgan
The Great Wall of Gorgan, also called the Gorgan Defense Wall, Anushirvan Barrier, Firuz Barrier and Qazal Al'an, and sometimes Sadd-i-Iskandar, (Persian for dam or barrier of Alexander) is an ancient defensive facility located in the Gorgan region of northeastern Iran, in Antiquity known as Hyrcania.Kiani, M. Y. Gorgan, iv. Archeology, Encyclopedia Iranica, Online version. 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. Larger than Hadrian's Wall and the Antonine Wall taken together, it is the greatest monument of its kind between Europe and China and it may be the longest brick, or stone, wall ever built in the ancient world. Omrani Rekavandi, H., Sauer, E., Wilkinson, T. & Nokandeh, J. (2008), The enigma of the red snake: revealing one of the worlds greatest frontier walls, Current World Archaeology, No. 27, February/March 2008, pp. 12-22. PDF 5.3 MB. p. 13
The barrier consists of a wall, 155 kilometres long and 6 to 10 metres wide, along the length of which are located a number of fortresses, spaced at intervals of between 10 and 50 kilometres. 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 Gonbade Kavous, continues towards the northwest, and vanishes behind the Pishkamar Mountains. A logistical archaeological survey was conducted regarding the wall in 1999 due to problems in development projects, especially during construction of the Golestan Dam, which irrigates all the areas covered by the wall. At the point of the connection of the wall and the drainage canal from the dam, architects discovered the remains of the above wall. 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. Due to many difficulties in development and agricultural projects, archaeologists have been assigned to mark the boundary of the historical find by laying cement blocks.
Attention must be likewise given to a similar Sassanian defense wall and fortification on the opposite side of the Caspian Sea at the port of Derbent and beyond. Where the Great Wall of Gorgan continues into the Sea at the Gulf of Gorgan, on the far side of the Caspian emerges from the Sea the great wall of Caucasus at Derbent, complete with its extraordinarily well preserved Sassanian fort.
While the impressive fortification and walls on the east side of the Caspian Sea remained unknown to the Graeco-Roman historians, the western half of this impressive "northern fortifications" in the Caucasus were well known to the Classical authors.
Dr. Kiani who led the archaeological team in 1971 believed that the wall was built during the Parthian dynasty 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.
"If we assumed 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, all the more remarkable as our investigations focused just on 200km of vulnerable frontier, a small fraction of the thousands of kilometres of borders of one of the ancient world's largest empires."
Gates of Alexander
Cyrus the Great in the Qur'an
First Iranian Defensive Wall: The Great Wall of Gorgan: A Research Article by Manouchehr Saadat Noury