Mongolian Script

The Mongolian vertical script was developed as an adaption of the Uyghur script to write the Mongolian language. It was introduced by the Uyghur scribe Tatar-Tonga, who had been captured by the Mongols during a war against the Naimans around 1204. There were no substantive changes to the Uyghur form for the first few centuries, so that, for example, initial yodh stood for both [dʒ] and [j], while medial tsadi stood for both [dʒ] and [tʃ], and there was no letter for [d] in initial position. Mongolian sources often distinguish the early forms by using the term Uyghurjin script (Chinese: 回鹘式蒙古文, Mongolian for Uyghur style script). Western sources tend to use this term as a synonym for all variations of the Mongolian script.

Eventually, minor concessions were made to the differences between the Uyghur and Mongol languages: In the 17th and 18th centuries, smoother and more angular versions of tsadi became associated with [dʒ] and [tʃ] respectively, and in the 19th century, the Manchu hooked yodh was adopted for initial [j]. Zain was dropped as it was redundant for [s]. Various schools of orthography, some using diacritics, were developed to avoid ambiguity.

Mongolian is written vertically. The Uyghur script and its descendants—Mongolian, Oirat Clear, Manchu, and Buryat—are the only vertical scripts written from left to right. This developed because the Uyghurs rotated their Sogdian-derived script, originally written right to left, 90 degrees counterclockwise to emulate Chinese writing, but without changing the relative orientation of the letters.