 Another influence of the Liao cultural tradition is seen in the Yuan dynasty 's <unk> ( <unk> ) theater , its associated orchestration , and the qu ( <unk> ) and <unk> ( <unk> ) forms of Classical Chinese poetry . One documented way in which this influence occurred was through the incorporation of Khitan officers and men into the service of the Mongol forces during the first Mongol invasion of 1211 to 1215 . This northern route of cultural transmission of the legacy of Liao culture was then returned to China during the Yuan dynasty . 
