Tarzan and the Lost Empire - Edgar Rice Burroughs

The disappearance of a noted archaeologist hunting the secret of the Lost Tribe of the Wiramwazi Mountains was a signal to the one man who could penetrate Africa's deepest interior—Tarzan of the Apes. For only Tarzan, the white man who had been raised by the anthropoid apes, could understand the ways of the jungle and its beasts perfectly enough to speed to the scientist's rescue. But this time, in addition to savage tribes and vicious beasts, Tarzan uncovered a strange lost land—twin cities of Roman soldiery, outposts of a ruthless empire that had fallen fifteen hundred years before. Tarzan's desperate struggle between ancient intrigues and modern schemers, against deadly gladiators and enraged lions, is Edgar Rice Burroughs at his very best. - Summary by Original Gutenberg text