The devastating defeat of the flower of the English aristocracy at Bannockburn in 1314 has long cast a spell over medieval military historians. Despite the incessant warfare of the late thirteenth and fourteenth centuries, large battles were rare in this period. Anglo-Welsh and Anglo-Scottish warfare repeatedly pitched forces of unequal strength against one another, and only the most foolhardy opponents of Edwardian conquest, such as William Wallace, were willing to risk the lives of their fellow countrymen, and their long-term political objectives, in full-scale engagement. Therefore it is not surprising that this battle, which undermined the apparent invincibility of the English heavy cavalry, and which saw an unpopular king of England being driven from Scotland by a patriotic hero, has received so much attention from historians. Unfortunately the difficulties involved in trying to reconstruct the composition of the English army that was crushed at Bannockburn are immense. The loss of nearly all documentation giving details of the cavalry force that served in 1314 means that we can do little more than make informed guesses about the size, structure and composition of Edward II's force. In this paper I aim to provide a much more detailed account of an English army that served in Scotland just four years earlier, and for which the military service records are more revealing. The evidence relating to the Scottish campaign of 1310–11 might well hold the key to a better understanding of English military institutions on the eve of Bannockburn.