八思巴文
There are only two types of vertical scripts known to have been written from left to right: the Old Uyghur script and its descendants — Traditional Mongolian, Oirat Clear, Manchu, and Buryat — and the 'Phags-pa script. The former 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. 'Phags-pa in turn was an adaptation of Tibetan script written vertically on the model of Mongolian to supplant those writing systems current in the Mongol Empire. Of these, only traditional Mongolian still remains in use today in Inner Mongolia.