The ancient region of Toos, which is now within the city limits of Mashhad, used to be part of Greater Khorasan Territory. Ancient Toos dates to before Alexander the Great (356-323 BCE) and was once the capital of ancient Parthia known as Susia. Toos was situated on the Royal Highway, which was a part of the Silk Road. Consequently, Toos was a target for many military campaigns and was captured and destroyed by Alexander the Great (330 BCE), and then the Umayyad Caliphate (647 CE). Ancient Toos was also destroyed by Subutai, the Mongol general (1220 CE), and fought over by the Persians and Uzbeks in the 16th to 18th centuries.