As dawn broke on Saturday 20th May 1217, a small force of some 700 troops marched to war, hoping to save England from ruination. Their commander, William Marshal – a man fêted as ‘the greatest knight in all the world’ — sought to stiffen their resolve on that bright sun-lit morning, exhorting them to seize this “chance to free our land” and thereby earn “eternal glory”. Yet, in truth, their prospects were bleak. They would be heavily outnumbered by the enemy, perhaps as much as two-to-one, and though Marshal may have been the finest warrior of the age, at seventy he was entering his dotage. Nonetheless, the fate of the realm rested on their shoulders that day. The battle they fought would be the most significant waged on English soil since 1066, and its outcome would reshape the kingdom’s history.