William of Poitiers became a chaplain in the household of William the Conqueror, and was able to give a first-hand account of the events of 1066-7. The Gesta Guillelmi, his unfinished biography of the king, is particularly important for its detailed description of William's campaigns in Normandy, the careful preparations he made for the invasion of England, the battle of Hastings, and the establishment of Norman power after the Conquest. It is a mine of information of military tactics and the conduct of war in the eleventh century. Though written from the point of view of the Norman court, it...