The documents in this volume were written by people of the West Uighur kingdom, which flourished from the second half of the 9th century to the start of the 13th century in and around the eastern Tianshan region including the Turfan Depression, and by Uighurs of the 13th to 14th centuries when this region had come under the rule of the Mongol empire (i.e. former West Uighurs). Old Uighur is a form of Old Turkic. This Corpus includes over two hundred letters that were written in Old Uighur using the Uighur script, which derives from the Sogdian script. Although the use of paper had at the time not yet spread to Europe, these letters are all written on paper. The ink is similar to that which was used in China, but the letters were written with reed or wooden pens rather than with writing brushes. The majority of these letters were discovered in the 20th century in China, either in the Turfan Depression in the Xinjiang Uighur Autonomous Region or in the famous Mogao Caves of the Thousand Buddhas at Dunhuang in Gansu, and a small number were unearthed at the remains of Kara-khoto in the Gansu Corridor.
