 Tarzan in his search for Erich von Harben finds a lost remnant of the Roman Empire hidden in the mountains of Africa.They are inhabitants of two rival cities Castra Sanguinarius, ruled by Sublatus Imperator, and Castrum Mare, ruled by Validus Augustus.Erich von Harben was captured and brought to Castrum Mare, where he meets Mallius Lepus, who takes him to his uncle, Septimus Favonius, introducing him as a barbarian from Germany.