Can you stop using the picture with nake warrior? That is wrong, because the invasion of Mongol in january to april, it is cold season with the temperature below 10 census, also in both Dai Viet history docucment and Yuan history document, both armies are light to heavily armoured soldiers, non of them are even half-nake, and the turban on Dai Viet soldiers only appear during 17th century and later. Also, the Mongol already face war elephant during Champa, Java campaign before Dai Viet campaign and Dai Viet's war elephant is inferior in number when compare to Champa, Dai Viet never use war elephant as sock cavalry but as general's bodyguard. Also mountain/jungle in northern Vietnam is not as much as Champa (middle region modern Vietnam), thus most of battles (95%) happened on river delta and rivers/sea.