Tus was an ancient city in Khorasan near the modern city of Mashhad, Razavi Khorasan province, Iran. To the ancient Greeks, it was known as Susia. It was also known as Tusa. The area now known as Tus was divided into four cities, Tabran, Radakan, Noan and Teroid, which in combination formed largest city in the region in the fifth century.