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 corner of the Caspian Sea . The western , Caspian Sea , end of the wall is near the remains of the fort at : ; the eastern end of the wall , near the town of Pishkamar , is near the remains of the fort at : . The title coordinate is for the location of the remains of a fort midway along the wall . 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 northern steppes to the Iranian heartland . The wall is believed to have protected the Sassanian Empire to the south from the peoples to the north . It is long and wide , and features over 30 fortress es spaced at intervals of between . It is surpassed only by the Great Wall of China as the longest defensive wall in existence . Among archaeologists the wall is also known as " The Red Snake " due to the colour of its bricks . It is also known as the Gorgan Defence Wall , Anushirvân Barrier , Firuz Barrier and Qazal Al ' an , and 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 . Description . The barrier consists of a wall , long and wide , with over 30 fortress es at intervals of between . The wall is made of standardized bricks , made from the local loess soil , and fired in kilns along the line of the wall . The wall lies slightly to the north of a local river , and features a ditch that conducted water along most of the wall . This wall starts from the Caspian coast , circles north of Gonbade Kavous , continues towards the northeast , and vanishes in the Pishkamar Mountains . In 1999 a logistical archaeological survey was conducted regarding the wall due to problems in development projects , especially during construction of the Golestan Dam , which irrigate s 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 Great Wall of Gorgan . 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 . Larger than Hadrian ' s Wall and the Antonine Wall taken together ( two separate structures in Britain that marked the northern limits of the Roman Empire ) , it has been called the greatest monument of its kind between Europe and China . The wall is second only to the combined walls that make up the Great Wall of China as the longest defensive wall in existence , and although now in substantial disrepair , it was perhaps even more solidly built than the early forms of the Great Wall . Route . The route , from east to west , is represented by the coordinates of the remains of the following forts and other features which lie along the wall . The coordinates and fort numbers , etc . are from Wikimapia : East end of wall West end of wall Dating . Dr . Kiani , who led the archaeological team in 1971 , believed that the wall was built during the Parthian Empire ( 247 BCE – 224 CE ) , and that it was restored during the Sassanid era ( 3rd to 7th century AD ) . 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 ( location of a drowned fort at the northern end : ; location of a fortlet or watchtower at the inland end : ) ; OSL and radiocarbon dating indicated a date for both walls in the late 5th or 6th century AD . These dates suggest that the current wall , at least , is Sassanid rather than Parthian , and that the current structure did not yet exist , some 800 years earlier , in the time of Alexander the Great ( died 323 BC ) . If Alexander encountered a barrier at this location it was a predecessor of the current wall . 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 . The Derbent Caspian Gate . A similar Sassanian defence wall and fortification lies on the opposite , western , side of the Caspian Sea at the port of Derbent , in the Republic of Dagestan , Russia . There the remains of a line of fortifications run inland for some from the shore of the Caspian Sea ( ) to what is today an extraordinarily well preserved Sassanian fort ( ) on the first foothills of the Caucasus mountains . Derbent and its Caspian Gates are at the western part of the historical region of Hyrcania . While the fortification and walls on the east side of the Caspian Sea remained unknown to the Graeco - Roman historians , the western half of the impressive " northern fortifications " in the Caucasus were well known to Classical authors .