Environmental concerns are relatively recent. Ancient armies would have little or no concept that they caused environmental damage. Such armies were ‘eco-warriors’ nevertheless, but in the sense of against the ecosystem, not for it. An army’s success may result from marching on its stomach, but what those stomachs produced could also conduct environmental warfare. Surprisingly little has been published about ancient armies’ daily bodily waste – urine and faeces – or the environmental impact where they encamped. An encamping army would cause rapid local and increasingly extending environmental change and devastation. Woodland would be steadily consumed, water security a constant concern, disease from pollution a threat. Food supplies would be sucked into camps from nearby and increasingly further afield. As for a camp’s growing smell, an enemy’s nose would have been more than adequate to find their foe. Using the example of Roman armies in the succession of camps mainly associated with the 2nd century BC campaigns against the Celtiberian city of Numantia, Spain, eye-watering sewage statistics emerge for when an army encamped, and its general environmental impact.