Costain's technique is essentially the same in William the Conqueror as it is in his historical novels for adults. He performs exhaustive research into the background of his subject to find authentic details. William the Conqueror is filled with specifics, including technical terms for weapons, an analysis of military tactics, and descriptions of clothing styles. Costain even includes information about which social classes could use specific types of hunting birds. By blending general historical research with specific biographical fact, Costain enhances the realism of his settings and his action.

But William the Conqueror is also a fictionalized biography. Costain builds upon the few known details of William's life to create a vivid, believable character. Indeed, much of Costain's material must be described as speculative. Although Costain does not tamper with historical fact, he constantly introduces dialogue or internal monologues for which no evidence exists. As a...