In "The Secret History of the Mongols", the Naiman subtribe the "Güchügüd" are mentioned. According to Russian Turkologist Nikolai Aristov's view, the Naiman Khanate's western border reached the Irtysh River and its eastern border reached the Mongolian Tamir River. The Altai Mountains and southern Altai Republic were part of the Naiman Khanate. They had diplomatic relations with the Kara-Khitans, and were subservient to them until 1175. In the Russian and Soviet historiography of Central Asia they were traditionally ranked among the Mongol-speaking tribes. For instance, such Russian orientalists as Vasily Bartold, Grigory Potanin, Boris Vladimirtsov, Ilya Petrushevsky, Nicholas Poppe, Lev Gumilyov, Vadim Trepavlov classified them as one of mongol tribes. Other scholars classified them as a Turkic people from Sekiz Oghuz (means "Eight Oghuz" in Turkic). However, the term "Naiman" has Mongolian origin meaning "eight", but their titles are Turkic, and they are thought by some to be possibly Mongolized Turks. They have been described as Turkic-speaking, as well as Mongolian-speaking. Like the Khitans and the Uyghurs, many of them were Nestorian Christians or Buddhists.