The "Divar-e Gorgan" (Persian for "The Great Wall of Gorgan") is a gigantic defensive wall built in the
Sasanian period of Iranian history. The visible remains are about long and wide. It is one of the most outstanding and gigantic architectural monuments in northeast Iran and the most impressive in the
Golestan Province. This wall, which is the largest defensive wall in the world after the
Great Wall of China, starts from the Caspian sea coast, circles north of the city of Gonbad-e Kāvus, continues towards the northeast, and vanishes into the
Pishkamar Mountains. At certain points, the Divar is wide and in other parts the width is , depending on the nature of the land and the soil type. Watch towers and forts had been built at varying distances. The longest distance between forts is and the shortest is . The 40 identified forts vary in dimension and shape but the majority are square fortresses. 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. The Divar defensive wall has also been known variously as Alexander Dam, Anushirvân Dam, Firuz Dam and Golestan's Defense Wall in various historical texts. Dr. Kiani, who led the archaeological team in 1971, believes that the wall was built during the Parthian dynasty, simultaneously with the construction of the Great Wall of China, and that it was restored during the
Sassanid era (3rd to 7th centuries AD). ==Neolithic period==