Classical Mongolian was a literary language of Mongolians, which was first introduced by the last Khan of Mongols when he set his clergy the task to translate all the Tibetan Buddhist Canon into Mongolian in 17th century.
This script then became the established literary language used for all Mongolian literature since its introduction, until 1930s and 1940s when then USSR's satelite nation, Mongolian People's Republic decided to change the Mongolian writing system from traditional Mongolian script to cyrillic alphabet.
The classical or traditional Mongolian script,also known as the Qudum Mongγol bičig,was a first writing system created specifically for the Mongolian language, and was the most widespread until the introduction of Cyrillic in 1946. It is traditionally written in vertical lines Text direction Top-Down, right across the page. Derived from the Old Uyghur alphabet, Mongolian is a true alphabet, with separate letters for consonants and vowels. The Mongolian script has been adapted to write languages such as Oirat and Manchu.
Alphabets based on this classical vertical script are used in Inner Mongolia and other parts of China to this day to write Mongolian, Xibe and experimentally, Evenki.
By Anand.orkhon - Own work, CC BY-SA 4.0, Link