Tarzan is asked by an old friend to find his son Erich Von Harben. Tarzan’s trail lead him to discover another lost civilization. This one was formed by a lost expedition of Romans and they have formed a civilization based on the old Roman Empire. Tarzan gets captured by one city while Von Harben the rival city. Both have adventures in the gladiator arenas but eventually overthrow the corrupt caesars for both cities.
The twelfth book in the series and there does seem to be a pattern to the stories. Tarzan can’t throw a stick without hitting a lost civilization. The civilizations are always some old transplanted ancient European type people divided into two warring factions. It doesn’t take into the fact that Europeans couldn’t enter Africa without dying of malaria until the vaccine was invented in the 1880’s. He would use this for another four or five books.
Still it seemed to be a formula that works. Suspending disbelief the stories are full of fast paced action that moves along at a brisk pace. I suppose that Africa in the 1920-30’s was a large mysterious place. I personally enjoy the image of an Africa filled with such lost civilizations. Makes for a good story.