 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 <unk> valley ( in present @-@ day <unk> Prefecture ) or 110 km southwest at <unk> ( present @-@ day <unk> , <unk> Prefecture ) , which the Burmese called <unk> . 
