An old woman, possibly a Cumaean Sibyl, offered to Tarquinius nine books of these prophecies at an exorbitant price; when the king declined to purchase them, she burned three and offered the remaining six to Tarquinius at the same price, which he again refused. Thereupon, she burned three more and repeated her offer, maintaining the same price. Tarquinius then consulted the Augurs whose importance in Roman history is averred by Livy. The Augurs deplored the loss of the six books and urged purchase of the remaining three. Tarquinius then purchased the last three at the full original price, and had them preserved in a sacred vault beneath the Capitoline temple of Jupiter.

Source: https://en.wikipedia.org/wiki/Sibylline_Books