Mr. Ellacott has previously chronicled the evolvement of the soldier from prehistory to the present (Spearman to Minuteman, Conscripts on the March, both 1966): here he focuses on the events preceding, attending and following the Norman Conquest with equal vitality, authority and use of evocative detail. This is political and military history in the large sense: It subsumes information about weapons and armor, laws and administration, sympathies and hostilities among the great and the common, sex and morals. Yes, sex--illegitimacy is treated as a social phenomenon and a political reality. The author probes inconsistencies -- ""Normans of the mid-eleventh century showed a curious mixture of religious fervor, illiteracy and sheer brutality"" -- and spots ironics with sometimes amused discernment. The drawings include maps, historical scenes, diagrams and details. Altogether, it's in the solid tradition of British historical writing, flavored by Mr. Ellacott's acquaintance with the interests of young people, and the fullest treatment available for this age group.