This ancient wall once stretched 190km from the Golestan Mountains to the Caspian Sea; like its equivalents in China and England, Alexander’s Wall was built to keep out warlike raiders from the north. For the Sassanian-Iranian world it marked the very real edge of civilisation: being banished beyond was equivalent to capital punishment. Comprehensively cannibalised for building materials over many centuries, only muddy undulations remain, though a relatively recognisable section runs along the northern side of the Haji Qoshan–Tamar road.
There were once around a dozen square guard-forts along the wall's length; the outline of several are still easy to make out, rising several metres above the surrounding plain. Most notable are fort #4 at Malaisheikh (10km west of Tamar) and fort #6, 500m off the road 4km west of Haji Qoshan village.
Research suggests that the wall and its forts date mostly from the 6th century AD, making its nickname referring to Alexander the Great appear to be romantic fiction. The local Turkmen population call it the more descriptive Qezel Alam ('Red Snake').