Tarzan, Lord of the Jungle

by Edgar Rice Burroughs

Tarzan finds an outpost of European knights and crusaders from a "forbidden valley" hidden in the mountains, whose ancestors had gone astray en route to the Holy Land and ended up in the depth of Africa. The 20th century ones still maintain a Medieval European way of life, having split into two mutually-hostile factions. Tarzan's lion ally Jad-bal-ja puts in an appearance late in the book.