 During the Tang dynasty (618–907), the area was formally designated "Hebei" (north of the Yellow River) for the first time.During the earlier part of the Five Dynasties and Ten Kingdoms period, Hebei was fragmented among several regimes, though it was eventually unified by Li Cunxu, who established the Later Tang (923–936).The next dynasty, the Later Jin under Shi Jingtang, posthumously known as Emperor Gaozu of Later Jin, ceded much of modern-day northern Hebei to the Khitan Liao dynasty in the north; this territory, called the Sixteen Prefectures of Yanyun, became a major weakness in the Chinese defense against the Khitans for the next century, since it lay within the Great Wall.