The Sibylline Books were the old prophecy records of ancient Rome. They were lost when the Roman empire came to an end, and are believed to have been burned. However Octavian, the Camp Jupiter augur does not seem to think that they have been destroyed completely, but has been declined of his requests to find them.
There is a theory that Ella the harpy, who had memorized and read multiple books, read the Sibylline Books.
- The Greek counterpart of the books may be the Oracle at Camp Half-Blood.
- It is hinted that Ella, the harpy, has memorized parts of the Sibylline Books. And thus also recites prophecies. (As mentioned throughout the Heroes of Olympus.)
- Octavian stated that the Sibylline Books has foretold the Prophecy of Seven for several thousands of years already. While the Greek demigods have only known the prophecy for less than a year.
- The books are said to predict the fate of Rome, which is why Octavian strives to obtain them and gain access to looking into the future or other dark purposes.