Ammianus Marcellinus Res Gestae 19.9.9

[9] But the king, although making a show of ease of mind in his expression, and to all appearance seeming to exult in the destruction of the city, yet in the depths of his heart was greatly troubled, recalling that in unfortunate sieges he had often suffered sad losses, and had sacrificed far more men himself than he had taken alive of ours, or at any rate had killed in the various battles, as happened several times at Nisibis and at Singara; and in the same way, when he had invested Amida for seventy-three days with a great force of armed men, he lost 30,000 warriors, as was reckoned a little later by Discenes, a tribune and secretary, the more readily for this difference: that the corpses of our men soon after they are slain fall apart and waste away, to such a degree that the face of no dead man is recognisable after four days, but the bodies of the slain Persians dry up like tree-trunks, without their limbs wasting or becoming moist with corruption-a fact due to their more frugal life and the dry heat of their native country.