At the Battle of Evesham (4 August 1265) the army of Simon de Montfort, earl of Leicester, was annihilated and his body dismembered, his head, testicles, a hand and a foot taken as ‘dark trophies’ by his enemies. The battle ended the ‘first English revolution’, in which a party of barons and bishops seized control of government from King Henry III and established a council to rule England. This article addresses the treatment of Simon’s remains. First, it considers critical evidence, the Opusculum de nobili Simone de Monte Forti, a tract produced in support of Simon’s cult at the Cistercian abbey of Melrose. Revealing how the Opusculum was researched and sponsored, it roots the vitality of Simon’s cult in the Anglo-Scottish borders, in the affinity with ancient Northumbria of the cross-border network that contributed to the tract. Secondly, it deploys the Opusculum to examine the Evesham dark trophy process, locating it within the socio-military culture of the Anglo-Welsh marches. Thirdly, it shows how the treatment of Simon’s body was implemented in response to a Montfortian policy of expediency that attempted the takeover of the Welsh Marches in alliance with the Welsh. It was not only England’s constitutional future at stake in August 1265, but also the balance of power in the British Isles. The first English revolution should thus be placed in the context of a British, rather than an English, war.