Tarzan and the Jewels of Opar by Edgar Rice Burroughs

Swinging back through the jungle in a wide circle the ape-man came to the river at another point, drank and took to the trees again and while he hunted, all oblivious of his past and careless of his future, there came through the dark jungles and the open, park-like places and across the wide meadows, where grazed the countless herbivora of the mysterious continent, a weird and terrible caravan in search of him. There were fifty frightful men with hairy bodies and gnarled and crooked legs. They were armed with knives and great bludgeons and at their head marched an almost naked woman, beautiful beyond compare. It was La of Opar, High Priestess of the Flaming God, and fifty of her horrid priests searching for the purloiner of the sacred sacrificial knife.

Never before had La passed beyond the crumbling outer walls of Opar; but never before had need been so insistent. The sacred knife was gone! Handed down through countless ages it had come to her as a heritage and an insignia of her religious office and regal authority from some long-dead progenitor of lost and forgotten Atlantis. The loss of the crown jewels or the Great Seal of England could have brought no greater consternation to a British king than did the pilfering of the sacred knife bring to La, the Oparian, Queen and High Priestess of the degraded remnants of the oldest civilization upon earth. When Atlantis, with all her mighty cities and her cultivated fields and her great commerce and culture and riches sank into the sea long ages since, she took with her all but a handful of her colonists working the vast gold mines of Central Africa.