According to the Yuan dynasty chronicle and Marco Polo 's accounts , a Burmese army " invaded " the Mongol territory of Gold Teeth , and was defeated by the Mongol army in April 1277 . The battle took place either at the Vochang valley ( in present @-@ day Baoshan Prefecture ) or 110 km southwest at Kanngai ( present @-@ day Yingjiang , Dehong Prefecture ) , which the Burmese called Ngasaunggyan .