The Saka were known as the Sak or Sai () in ancient Chinese records. These records indicate that they originally inhabited the Ili and Chu River valleys of modern Kyrgyzstan and Kazakhstan. In the Book of Han, the area was called the land of the Sak, i.e. the Saka. The exact date of the Sakas' arrival in the valleys of the Ili and Chu in Central Asia is unclear, perhaps it was just before the reign of Darius I. Around 30 Saka tombs in the form of kurgans (burial mounds) have also been found in the Tian Shan area dated to between 550-250 BC. Indications of Saka presence have also been found in the Tarim Basin region, possibly as early as the 7th century BC. At least by the late 2nd century BC, the Sakas had founded states in the Tarim Barin.