'Phags-pa script
The phonology of Old Mandarin has been inferred from the 'Phags-pa script, an alphabet created in 1269 for several languages of the Mongol empire, including Chinese, and from two rime dictionaries, the "Menggu Ziyun" (1308) and the "Zhongyuan Yinyun" (1324). The rhyme books differ in some details but show many of the features characteristic of modern Mandarin dialects, such as the reduction and disappearance of final stops and the reorganization of the four tones of Middle Chinese.