From a now discontinued blog by a Canadian, Robin Rowland:
The main theme of many of Rosemary Sutcliff’s books is the life of the soldier. Her father was a naval officer and she grew up in a military atmosphere. Although she was physically handicapped and spent part of her life in wheel chair, she captures the uncertain life of the intelligent human being who must become a fighter whether a member of a regular armed force or a warrior band or an individual trying to survive.
Sutlcliff had a unique viewpoint on the military, the insider who is also a somewhat removed observer, a combination of the kid sister although she had no siblings, the know-it-all cousin or neighbor, and the chronicler somewhat like Princess Irulan in Dune. Marcus Aquila Flavius thought he would be a career soldier, then finds the wound in his leg has changed his life….a fact of life facing many soldiers today. His descendent, Aquila, deserts his army to defend his home, becomes a slave and suffers throughout his life with what would, a millenia and half later, be called post traumatic stress disorder. Her soldiers are rounded human beings, with conflicting loyalties mixed with personal and family problems, always facing uncertainty in campaigns.
An academic might say that all this was reflection of the decline of the British Empire. Sutlcliff had liked Kipling as a kid and it could be said that her books are the Kipling stories of that declining empire. But as our society has become more uncertain in the years since she wrote, the books are more relevant than ever.