"Tarzan and the City of Gold" (Tarzan #16) by Edgar Rice Burroughs

When Tarzan of the Apes freed the white man who was being tortured by the savages, he was surprised to learn that the stranger came from no race or country the ape-man knew. He was from the fabled land of Onthat, where lay two ancient cities unknown to the outside world. One was Athne, city of ivory; the other was Cathne, city of gold and evil. There, great prides of trained lions were used to hunt down men and wage eternal war. And there Tarzam met the beautiful queen Nemone, who was determined to have Tarzan as her king...or feed him to the lions!