Orkhon (ôrˈkŏn, ôr-khŏnˈ) [key], river, c.300 mi (480 km) long, rising in the Khangai Mts., N central Republic of Mongolia, and flowing east, then north, past the site of ancient Karakorum, and then northeast to join the Selenga River just S of the Russian border. It is navigable for shallow-draft vessels only during July and August. The Orkhon Inscriptions, discovered in 1889 by the Russian explorer N. M. Yadrinstev near the site of ancient Karakorum, date from the 8th cent. They comprise minor Chinese texts and the oldest known material in a Turkic language. They were studied in 1891 by the Russian turkologist V. V. Radlov and were deciphered by the Danish philologist Vilhelm Thomsen in 1896.