Theophylact Simocatta, a historian during the reign of Heraclius (r. 610–641 AD), wrote that Taugast (or Taugas) was a great eastern empire colonised by Turkic people, with a capital city 2400 kilometers northeast of India that he called Khubdan (from the Turkic word Khumdan used for the Sui and Tang capital Chang'an), where idolatry was practised but the people were wise and lived by just laws.