The cross-cultural focus of the novel makes it socially relevant today. Sutcliff depicts the clash of the Celtic and the Roman cultures with sensitivity and appreciation for the unique strengths of each. The loyalty that the Seal People have to their gods of darkness and the power that the Druids have over the British tribes mirror Marcus's devotion to his god, Mithras. These warlike gods lead their followers to death and violence in the name of defending their ways of life, but the novel does not glorify war.

Scenes of violence are minimal, and honor, courage, and loyalty are stressed.

On an individual basis, the characters confront others as human beings whom they can respect despite their differences. Marcus learns to tolerate cultural differences, and in the end, he abandons plans to return to Italy and chooses to make Britain his home.