The Sibylline Books were a collection of prophecies in rhyme written in Greek. The legendary king of Rome, Tarquinius Superbus bought them from a Sibyl (a kind of prophetess), and the prophecies used to be consulted in times when great danger happened in the history of the Roman Empire.

History 
The books were also known to the Greeks. They were kept in the Temple of Apollo at Gergis on Mount Ida (near Troy in Asia Minor) in the 7th century BC, and said to be written by the Hellespontine Sibyl. From there, it passed to Erythrae (in eastern Asia Minor) and was called the work of the Erythraean Sibyl. It seems that this collection travelled from there to Cumae, Italy and from there to Rome. 

According to Virgil in the Aeneid, Aeneas had consulted the Cumaean Sibyl before he travelled to the lower world. The story of how king Tarquinius bought them from the Cumaean Sibyl was a famous legend. She offered to sell Tarquin a collection of nine books of prophecy, but he refused the price, so she burnt three. After that she offered to sell the six remaining books for the same price. He refused again and she burnt another three. Finally he bought these three remaining books for this price so they would not be destroyed, and put them in the temple of Jupiter in Rome. 

The books were given to the trust of two Roman patricians (nobles). Beginning in 367 BC, ten keepers - five from the patricians and five from the common citizens - were appointed for them. After this (possibly the time of Sulla, 88-78 BC), the number of keepers was increased to fifteen. The job of these keepers was to consult the books on what was the right action or ceremony to escape from threats. Even so, they would not reveal the prophecies themselves, but only tell the action or ceremony needed.

The influence of the books brought eastern gods such as Apollo, the "Great Mother" Cybele, and Ceres, as well as Greek pagan beliefs, into the Roman pagan religion. 

Because the verses were written in Greek, the keepers would always be helped by two Greek translators. The books were destroyed when the Temple of Jupiter burned down in 83 BC. Because of this, the Roman Senate sent messengers in 76 BC to find similar prophecies and replace them. The prophecies were gathered especially from Troy, Erythrae, Samos island, 'Africa' (that is, modern Tunisia), and from Sicily and Tibur in Italy. After they brought the new collection to Rome, Roman priests separated what they thought was true, but threw others out of the collection. 

The Roman Emperor Augustus in 12 BC moved them to the Temple of Apollo, when they were studied and a new copy was made. They stayed there until 405 AD. It is said that at that time, Stilicho, who fought for the teachings of Arianism, burnt them. 

Modern scholars believe these books are not the same as the Sibylline Oracles that were often quoted by early Christian writers from the 2nd century through the 5th century AD. It is certain that when one Christian writer, Athenagoras of Athens, wrote A Plea for the Christians to Emperor Marcus Aurelius in around 176 AD, at a time when Christians were being punished by the pagan Roman Empire, he quoted word-for-word from these Oracles that are known today. Quoting them along with writings by Homer and Hesiod, he wrote many times that "these books are all known to Caesar" (the Emperor). The Sibylline Books were still to be found in the Temple of Apollo at Rome at this time, so it is thought possible that at least some of these Sibylline Oracles were partly the same. 

70 lines agreed to be from the real Sibylline Books were quoted in the 2nd century Book of Marvels by Phlegon of Trales. This quote speaks about the birth of a hermaphrodite, and ceremonies for sacrificing to idols.

Consultations recorded in history 

 238 or 240 BC: The 'Flower Games' (Ludi Florales) were started on the Books' advice.
 216 BC: When Hannibal, the Carthaginian general, destroyed a Roman legion at the battle of Cannae, the Books were consulted and on their advice, two Greeks and two Gauls were buried alive in the market of Rome.
 204 BC: In the Punic Wars, the Roman commander Scipio Africanus, on the Books' advice, brought the idol of Cybele from Pessinos and introduced her worship to Rome. 
 63 BC: A noble named Cornelius tried to take control in Rome because of a prophecy.
 44 BC: A prophecy that only a king could defeat Parthia caused rumors that Julius Caesar, head of the Roman Republic, wanted to become a king. 
 In the reign of Tiberius (14-37 AD), when the Tiber river flooded in Rome, one priest suggested that the Books be consulted, but Tiberius refused, because he thought they should stay secret. 
 AD 271: The Books were consulted after the Romans were defeated by the Germanic tribe Alamanni at the battle of Placentia.
 312: When the opposing generals Maxentius and Constantine I got ready to fight the Battle of the Milvian Bridge, Maxentius consulted the Sibylline Books and lost, while Constantine changed his faith from the pagan religion to that of the Christians, and won.

Other websites 
 An article about the Sibylline Books
 The Sibylline Oracles known to early Christians, translated from Greek

Roman mythology
Religious texts