Defensive Walls of Khorassan:The Pieces of a Defensive Continental Chain

Due to the geographic advantages, the extent region in center of Asia including northeastern Iran and northern Afghanistan has been attracted the populations since the first immigrations date to the 3rd millennium B.C. The region was traditionally defined as the great Khorassan was expanding from Transoxiana and Khwarezm in the north to Quhistan and Sistan in the south and from Pamir and Kashmir in the east to Qumes and Rayy in the west. Khorassan was situated on the chief route of Asia, Silk Road and was enjoying fertile plains and temperate climate. The favorable conditions of Khorassan have caused to formation settlements and to attract nomads who was migrating in central Asia in order to achieve a better living condition. Their arrival to Khorassan was sometimes associated with cruelly invasions. According to the historical reports, the first military contact between Persian kingdom and the invaders of northeastern Iran occurred in the reign of Cyrus the great in the 6th Century BC. The invasions from northeastern Iran continued during the reign of Seleucids and Arsacids and culminated by raids of Huns and Hephthalites in Sassanid era. The various groups of invaders including the tribes of Ghuzz, Seljuk, Mongol, Uzbek and Turkmen attacked northeastern Iran from the 7th to 20th Century. However, because of the physiographic conditions of northeastern Iran, it was not easily possible to access fertile plains and pastures of central Khorassan for many groups of northern nomads and invaders. The major natural barrier was a wall-like range in northeastern Iran named Kopet Dagh Mountains. The Kopet Dagh with an altitude of about 3000 meters above sea level in the highest point provides a natural wall extended from the east to the west of Khorassan. Nevertheless morphological attributes such as gorges and passes make some passageways across the Kopet Dagh range.  Crossing the Kopet Dagh moreover is possible through the eroded ridges. The traversable locations were controlled by defensive installations. An important type of the installations was the defensive walls restricting entrance to Khorassan and preventing sudden attacks to settlements called here the Defensive Walls of Khorasan. The defensive walls of Khorassan includes some disperse walls located in gorges and cols of the Kopet Dagh in Aq-Darband, Mozdouran and Kalat.
The aforementioned geographical conditions were extended to the other regions of Asia causing the populations of southern Asia to construct some similar walls along northern borders including the Great Wall of China, the walls of Central Asia, the Gorgan wall, and the Derbent wall, from east to west.
The conclusions demonstrate the strongly correlation between geographical position of the defensive walls and geographical landscape of Asia. The continuous terrain features including high mountains and deep seas provide an impenetrable barrier which separate the cultivator societies of southern from nomadic groups of northern Asia. Everywhere the natural barrier was passable the architectural walls such as the defensive walls of Khorassan, Gorgan, Derbent and China were been constructed.
However, a wall composed of physiographical features and architectural structures was stretched from Black Sea in the west to Yellow Sea in the east of Asia. The wall is introduced as The Long Wall of Asia and described in present paper for the first time. The Long Wall of Asia including the defensive walls of Khorassan with a total length of more than 11,000 kilometers demonstrate clearly the interaction between humans and the environment along history.