Orhon (or Orkhon) inscriptions are the oldest known Turkic writings, which were erected near the Orhon River between 732 and 735 in honour of two Kokturk princes named Kul and Bilge.
They have been carved on two monuments by old Turkic runes (see Orkhon script), which were deciphered by the Danish philologist Vilhelm Thomsen in 1893. Compared with monuments left by Tu-jue (突厥 pinyin tu2 jue2) in China during Tang Dynasty, the inscription was the fundamental proof of the equivalence of Gokturks and Tu-jue (突厥 pinyin tu2 jue2) as the alphabets are equivalent.
Inscriptions dating from the later 8th century AD in a slight variant of the Orkhon alphabet, known as Yenisei or Siberian runes, have also been found around Yenisei and other parts of Siberia.
The Orkhon alphabet is thought to have been derived from or inspired by a non-cursive version of the Sogdian script.
By the 9th century AD, the Orkhon and Yenisei alphabets were replaced by the Uighur alphabet, which developed from the cursive version of the Sogdian script.
The Orkhon Valley inscriptions were discovered by Nikolay Yadrintsev's expedition in 1889, published by Vasily Radlov and deciphered by the Danish philologist Vilhelm Thomsen in 1893.
The inscription corpus consists of two monuments which were erected in the Orkhon Valley between 732 and 735 in honour of the two Kokturk princes Kul Tigin and Bilge Khan, as well as inscriptions on slabs scattered in the wider area.
The Orkhon monuments are the oldest known examples of Turkish writings; they are inscribed on obelisks and have been dated to 720 (for the obelisk relating to Tonyukuk), to 732 (for that relating to Kültigin), and to 735 (for that relating to Bilge Kagan).