[3]: 84 He was apparently born in Les Préaux, France, near Pont-Audemer to an influential knightly Norman family, probably about 1020.
[4] According to Orderic, William originally trained as a knight, which gave him a much greater insight into the details of war than the typical medieval clerical writer.
Once he turned to the priesthood, William studied at the renowned school of Saint Hilaire-le-Grand in Poitiers and was said by Orderic to have returned to Normandy 'more learned than all his friends and neighbours'.
[4] However, he doesn't appear in any ecclesiastical or royal and ducal charters as might be expected from someone of such a position, which perhaps casts doubts over Orderic's account of William of Poitiers life.
[4] The Gesta Guillelmi is the earliest extended biography of any Duke of Normandy, and is an invaluable source for the Battle of Hastings in 1066.
R. Allen Brown writes: "Within the panegyric there is a wealth of facts and details... most derived from personal knowledge and personal contacts, compiled and intelligently put together by a man uniquely qualified as both clerk and knight, closely connected with the court ... One may add that William of Poitiers must have known his hero from their joint youth up, and stress that as both former knight and former chaplain of the duke he is able to bring us closer to the heart of Normandy in the mid-eleventh century than any other writer of that age or later.
'[7] Moreover, Orderic Vitalis, who uses the Gesta Guillelmi as his principal source in creating his 'Ecclesiastical History', chooses to omit or contradict many of Poitiers' passages in the Guesta Guillelmi, including denial of King William's mercy to the conquered English; having been brought up in England from 1075–1085, Orderic knew better.
However, the Gesta Guillelmi cannot be dismissed; most of the panegyrical passages are easy to isolate, and there is a lot of material that William of Poitiers probably reports accurately.
William of Poitiers believed that the pre-Conquest English 'all showed love of their country', suggesting some sort of national identity that was lacking in Normandy.
The local Norman lords constantly waging private wars contrasts with the relatively stable Anglo-Saxon Kingdom across the Channel.
An effective Duke could use them as strategic power bases, stamping their authority on the rural Duchy; however, a castle could also be a rallying point for rebellious nobles.