The Sibylline Books or Libri Sibyllini were a collection of oracular utterances, set out in Greek hexameters, purchased from a sibyl by the last king of Rome, Tarquinius Superbus, and consulted at momentous crises through the history of the Republic and the Empire. Only fragments have survived, the rest being lost or deliberately destroyed.
The Sibylline Books should not be confused with the so-called Sibylline Oracles, twelve books of prophesies thought to be of Judaeo-Christian origin.
According to the Roman tradition, the oldest collection of Sibylline oracles appears to have been made about the time of Solon and Cyrus at Gergis on Mount Ida in the Troad; it was attributed to the Hellespontine Sibyl and was preserved in the temple of Apollo at Gergis. From Gergis the collection passed to Erythrae, where it became famous as the oracles of the Erythraean Sibyl. It would appear to have been this very collection that found its way to Cumae (see the Cumaean Sibyl) and from Cumae to Rome.
The story of the acquisition of the Sibylline Books by Tarquinius, is one of the famous mythic elements of Roman history. At Cumae, Virgil has Aeneas consult the Cumaean Sibyl before his descent to the lower world (Aeneid VI, 10). The Cumaean Sibyl offered to Tarquinius nine books of these prophecies; and as the king declined to purchase them, owing to the exorbitant price she demanded, she burned three and offered the remaining six to Tarquinius at the same stiff price, which he again refused, whereupon she burned three more and repeated her offer. Tarquinius then relented and purchased the last three at the full original price and had them preserved in a vault beneath the Capitoline temple of Jupiter. The story is alluded to in Varro's lost books quoted in Lactantius Institutiones Divinae (I: 6) and by Origen.
The Sibylline Books were entrusted to the care of two patricians; after 367 BC ten custodians were appointed, five patricians and five plebeians, who were called the decemviri sacris faciundis; subsequently (probably in the time of Sulla) their number was increased to fifteen, the quindecimviri sacris faciundis. They were usually ex-consuls or ex-praetors. They held office for life, and were exempt from all other public duties. They had the responsibility of keeping the books in safety and secrecy. These officials, at the command of the Senate, consulted the Sibylline Books in order to discover, not exact predictions of definite future events in the form of prophecy, but the religious observances necessary to avert extraordinary calamities and to expiate ominous prodigies (comets and earthquakes, plague and the like). It was only the rites of expiation prescribed by the Sibylline Books, according to the interpretation of the oracle that were communicated to the public, and not the oracles themselves, which left ample opportunity for abuses.
In particular the keepers of the Sibylline Books had the superintendence of the worship of Apollo, of the "Great Mother" Cybele or Magna Mater, and of Ceres, which had been introduced by the Sibylline Books. Thus one important effect of the Sibylline Books was their influence on applying Greek cult practice and Greek conceptions of deities to indigenous Roman religion, which was already indirectly influenced through Etruscan religion. As the Sibylline Books had been collected in Anatolia, in the neighborhood of Troy, they recognized the goddesses and gods and the rites observed there and helped introduce them into Roman State worship, a syncretic amalgamation of national deities with the corresponding deities of Greece, and a general modification of the Roman religion.
Since they were written in hexameter verse and in Greek, the college of curators was always assisted by two Greek interpreters. The books were kept in the Temple of Jupiter on the Capitol, and when the temple burned in 83 BC, they were lost. The Roman Senate sent envoys in 76 BC to replace them with a collection of similar oracular sayings, in particular collected from Ilium, Erythrae, and Samos, Sicily and Africa. This new Sibylline collection was deposited in the restored temple, together with similar sayings of native origin, e.g. those of the Sibyl at Tibur (the 'Tiburtine Sibyl') of the brothers Marcius, and others. The priests then sorted them, retaining only those that appeared true to them (Tacitus, Annales, VI, 12). From the Capitol, they were transferred by Augustus as pontifex maximus in 12 BC, to the temple of Apollo Patrous on the Palatine, after they had been examined and copied; there they remained until about AD 405. According to the poet Rutilius Claudius Namatianus, the general Flavius Stilicho (died AD 408) burned them, as they were used to attack his government.
Some genuine Sibylline verses are preserved in the Book of Marvels or Memorabilia of Phlegon of Tralles (2nd century AD). These represent an oracle, or a combination of two oracles, of seventy hexameters in all. They report the birth of an androgyne, and prescribe a long list of rituals and offerings to the gods.