In 1324, about fifty years after the establishment of the Yuan dynasty, a rhyming book entitled Zhōngyuán Yīnyùn 中原音韻 ‘Rhymes of the Central Plain’ was published. The phonological system seen in this book is completely different from the Qièyùn system, but it shares many basic phonological characteristics with Modern Mandarin. Therefore, in the study of historical phonology, the Chinese of the Zhōngyuán Yīnyùn is referred to as Old Mandarin. The Zhōngyuán Yīnyùn documents a phonological system that had already existed in the north of China for centuries. Like the Qièyùn, it was not based on the phonology of any single dialect; the phonological distinctions could be from a variety of prestigious forms of Mandarin dialects at the time. This new standard represented an important turning point in the phonological history of Chinese. The Zhōngyuán Yīnyùn provides a complete phonology of the standard language based on the Zhongyuan dialect as indicated by the title of the book; however, the well-established phonological characteristics of the Zhōngyuán Yīnyùn suggest that the origin of Mandarin phonology should have been from a much earlier time.