It is mentioned as "Kophes" or "Kophene" in some classical writings. Hsuan Tsang refers to the city as "Kaofu" in the 7th century AD, which is the appellation of one of the five tribes of the Yuezhi who had migrated from across the Hindu Kush into the Kabul valley around the beginning of the Christian era. It was conquered by Kushan Emperor Kujula Kadphises in about 45 AD and remained Kushan territory until at least the 3rd century AD. The Kushans were Indo-European-speaking peoples based in Bactria (northern Afghanistan).