Sibylline Books

The Sibylline Books is a collection of prophecies that were used during Ancient Rome and of which only fragments have survived, the rest being lost, deliberately destroyed, or misplaced. Ella is the only known reader of the books and Octavian is desperately after them.

History
Passed down from an Oracle named the Sibyl of Cumae, the Sibylline Books are a collection of oracular utterances. The myth says the Sibyl came to Tarquin, the last Roman king, and offered nine books for an immense price. Tarquin simply sent her away and continued doing his work. The Sybil burned three of the books and offered them for the same price, which was promptly rejected. She burned three more and did the same thing with the same reaction. She burned two more and offered the last one for the same price. The king was very curious and he couldn't believe someone would offer him one book for such a huge price and finally decided to buy it. All of the prophecies effecting the Roman Empire were said to have been in these books, but they have been lost for centuries.

The Son of Neptune
The Sibylline Books are first mentioned when Percy Jackson asks if Camp Jupiter had an Oracle so they could be given a prophecy. Octavian, the augur, remarks that the idea of an Oracle was cute, but the camp didn't have one. Hazel Levesque then explains to Percy that the Sibylline Books are books of prophecy and that ancient Rome would consult them whenever there were any major disasters. However, it is widely believed the books burned when Rome fell.

Octavian counters that only some people believe that the books burned, but Reyna wouldn't authorize a quest (because she isn't stupid, according to Hazel). Camp Jupiter has a few scraps of the books safe, engraved on the marble floor of the Temple of Jupiter. One of these prophecies included the Prophecy of Seven, which Percy understands because Rachel Elizabeth Dare had recited it after becoming the Oracle.

Later, after Mars appears to the members of Camp Jupiter, he issues a quest. Octavian approaches him and says they need a prophecy from the Sibylline Books in order to issue a quest. Mars instead writes a prophecy for the quest and says they could add it to their books or engrave it on their floor with the other Sibylline Books' prophecies.

While on their quest to Alaska, Percy, Hazel, and Frank come across a Harpy named Ella, who is being tortured by the blind seer Phineas. While asking her questions, Ella speaks a few lines of prophecy, including the first Great Prophecy, and later, a prophecy about a son of Neptune drowning, but comments that the rest of the page was "burned." Hazel makes the connection that the burned book of prophecies Ella was talking about could be the Sibylline Books and concludes they need to keep her away from Octavian.

After returning to Camp Jupiter and defeating the Giant Army and Polybotes, Percy is elected Praetor, taking away Octavian's chance for power. Percy, Hazel, and Frank agree to protect Ella from Octavian, as with Percy now praetor, Octavian would look for other ways to extend his influence at Camp Jupiter, most likely by using his power of prophecy, and with Ella's knowledge of the Sibylline Books.

Trivia

 * It is hinted that Ella has memorized parts of the Sibylline Books as she also recites prophecies.
 * It is unknown where Ella read the book.
 * While the Sibylline Books are filled with prophecies that predict important events during the Roman Empire, Ella remembered reading the first Great Prophecy, a prophecy relating to the Greek demigods of Camp Half-Blood.
 * The books are said to have predicted the fate of Rome.