The Sixteen Prefectures , more specifically the Sixteen Prefectures of Yan and Yun or the Sixteen Prefectures of You and Ji , comprise a historical region in northern China along the Great Wall in present-day Beijing and Tianjin Municipalities and northern Hebei and Shanxi Province, that were ceded by the Shatuo Turk Emperor Shi Jingtang of the Later Jin to the Khitan Liao dynasty in 938. The subsequent Later Zhou and Song Dynasties sought to recover the ceded northern territories. Most of the Sixteen Prefectures including the two principal cities, Youzhou (also called Yanzhou, modern Beijing) and Yunzhou (modern Datong) remained in Liao hands until the 1120s, when the Jurchens of the Jin dynasty conquered the region. In 1123, the Jurchens ceded most of the territories except Yunzhou to the Song, but retook them in 1125. The loss of the Sixteen Prefectures exposed the plains of central China to further incursions by the Jurchens (the ancestor of Manchus) and the Mongols.