The traditional Mongolian script was born of conquest and adapted for scripture. The standard account places its adoption around 1204, when Genghis Khan defeated the Naiman and took into service the Uyghur scribe Tata-tonga, who taught the Uyghur alphabet to the Mongol court for the writing of decrees. The Uyghur script itself descended from Sogdian and ultimately from Aramaic, and the Mongols inherited its most distinctive habit turned through ninety degrees: the script runs in vertical columns from top to bottom, the columns proceeding left to right, a direction no other major living script uses.
Letters take initial, medial and final forms, and the early orthography fit Mongolian only roughly, which later reformers addressed with added diacritics and refined letterforms. The script wrote the chancery documents of the largest land empire in history, and the Secret History of the Mongols, though preserved in Chinese transcription, was composed in this written tradition. Kublai Khan commissioned the square Phags-pa script to replace it, but the vertical letters outlived the experiment and remained the Mongols' own writing, carried by the Oirat in a refined clear script offshoot and by the Manchus, who adapted it for their own imperial language.