The Khitans were a Turco-Mongol clan who dominated China north of the Yangtze River during the early mediaeval period. They adopted and then adapted many of the cultural traditions of their powerful neighbours to the south, the Song Chinese. However, before their absorption into the Mongol Empire in the late 13th century they proved pivotal, firstly in the eastward expansion of the armies of Chinggis Khan, secondly, in the survival of the Persian heartlands after the Mongol invasions of the 1220s and thirdly, in the revival and integration of the polity of Iran into the Chinggisid Empire. Da Liao, the Khitans, the Qara Khitai, names which have served this clan well, strengthened and invigorated the hosts which harboured them. The Liao willingly assimilated into the Chinggisid Empire of whose formation they had been an integral agent and in doing so they also surrendered their identity but not their history. Recent scholarship is now unearthing and recognising their proud legacy and distinct identity. Michal Biran placed the Khitans irrevocably and centrally in mediaeval Asian history and this study emphasises their role in the establishment of the Mongol Empire.