towers used to stretch for forty kilometers between the Caspian Sea and the Caucasus Mountains, effectively blocking the passage across the Caucasus. Derbent was built around a Sassanid Persian fortress, which served as a strategic location protecting the empire from attacks by the Gokturks. The historical Caspian Gates were not built until probably the reign of Khosrow I in the 6th century, long after Alexander's time, but they came to be credited to him in the passing centuries. The immense wall had a height of up to twenty meters and a thickness of about 10 feet (3 m) when it was in use. Darial The Pass of Dariel or Darial has also been known as the "Gates of Alexander" and is a strong candidate for the identity of the Caspian Gates. Wall of Gorgan An alternative theory links the Caspian Gates to the so-called "Alexander's Wall" (the Great Wall of Gorgan) on the south-eastern shore of the Caspian Sea, 180 km of which is still preserved today, albeit in a very poor state of repair. The Great Wall of Gorgan was built during the Parthian dynasty simultaneously with the construction of the Great Wall of China and it was restored during the Sassanid era (3rd–7th centuries) See also Sasanian defense lines Alexander in the Qur'an Cilician Gates Great Wall of China Iron Gate (Central Asia) Fortifications of Derbent Notes Explanatory notes Citations References Artamonov, Mikhail. "Ancient Derbent" (Древний Дербент). in: Soviet Archaeology'', No.8, 1946. External links Chapter 29 of the Travels of Sir John Mandeville, which includes the Gates of Alexander story Alexander the Great in legend Medieval legends Dhul-Qarnayn Gog and Magog History of Derbent