Left, the Roman Camp. 

White bell tent, ball apex (indeterminate colour) on pole, black apron, apex guy ropes, four heraldic shields decorate the roof (black eagle (spread winged) on gold background), panel definition on roof and walls, dark round re-inforcing at three point guy rope attachment points at top of valance, diamond shapes decorate the valance, one to the heraldic shields decorate the wall to the right of the door, separate door flap pulled to one side, decorated edges similar to door frame, the edges of the door frame are decorated with a row of dark triangles pointing away from the door, bluish pole with three dark shield shapes. 

White bell tent, ball apex on pole, red apron, apex guy ropes, panel definition on roof and walls, three point guy rope attachment (two above the valance and the other through the valance), valance in dark shade decorated by lettering ("Q, M, S"). 

White pavilion, two ball apexes on poles, dark apron, apex guy ropes ( at least three on front apex),  panel definition on roof and walls, heraldic shield on short side, decorated valance. 

Two darker (reddish) bell tents in rear, ball apexes on poles, reddish aprons, apex guy ropes, panel definition on roof (red lines). 

Right, the Barbarian camp. 

White bell tent, orange ball apex, dark reddish apron, apex guy rope, panel definition on roof and walls, three heraldic shields visible (red heaters, with gold lion rampart) decorate the roof, three point guy rope attachment to dark re-inforcements above valance, door flap and edge of door frame decorated with a row of dark triangles, patterned valance. 

Darker shade bell tent, ball apex, black apron with lines of spots, apex guy ropes, panel definition on roof and walls (in red lines), valance  decorated in red patterning, valance guy rope, some of the re-inforcements are visible. 

Three bell tent in rear, ball apexes on poles (reddy/yellow), two with black aprons, one with red apron (also with one, possibly two of the heraldic shields of on the roof, apex guy ropes.

"Saint Martin Renounces his weapons. To the left, the Roman camp, with Emperor Julian, a group of soldiers and the treasurer distributing money to the mercenaries." 

"...to the right waiting for the battle, behind the hill, the barbarian army with their armour and their spears."

SIMONE MARTINI - Italian painter, Sienese school (b. 1280/85, Siena, d. 1344, Avignon)