The Fortifications of Derbent (also transcribed as Darband) are one of the fortified defense lines built by the Persian Sasanian Empire to protect the eastern passage of the Caucasus Mountains (the Caspian Gates) against the attacks of the nomadic peoples of the Pontic-Caspian steppe. Built in the 6th century during the reign of Persian emperor Khosrow I and maintained by various later Arab, Turkish and Persian regimes, the fortifications comprise three distinct elements: the citadel of Naryn-Kala at Derbent, the twin long walls connecting it with the Caspian Sea in the east, and the mountain wall of Dagh-Bary, running from Derbent to the Caucasus foothills in the west. The immense wall, with a height of up to twenty meters and a thickness of about 10 feet (3 meters), stretched for forty kilometers between the Caspian Sea and the Caucasus Mountains, thirty north-looking towers stretched for forty kilometers between the Caspian Sea and the Caucasus Mountains, effectively blocking the passage across the Caucasus.