When the young German scholar Erich von Harben disappears in Africa’s Wiramwazi Mountains, Tarzan sets out to find him, while von Harben has already crossed into a hidden land where descendants of the Roman Empire still preserve their ancient institutions and rivalries. Following his trail, Tarzan discovers the existence of the two isolated Roman cities and enters Castra Sanguinarius, only to be treated as a barbarian, captured, and taken toward the arena for a deadly confrontation. Still separated, Tarzan and von Harben become entangled in political intrigue and struggles for power as their paths gradually converge within the forgotten empire.
