Explanation: The Sibylline Books were a series of cryptic and sacred verses that were left unread, except in times of extreme crisis. When the Senate called for the Sibylline Books to be read, they would be carefully taken from storage, a random page chosen, and verses read as prophecy. How those cryptic verses are interpreted is, of course, much more flexible.
During the Second Punic War, when the Republic seemed on the edge of destruction by the Carthaginian military genius Hannibal, the conclusion from reading the Sibylline Books was to commit human sacrifice by burying four foreigners alive - two Greek slaves, and two Gallic slaves. Traditionally, human sacrifice was regarded as odious and offensive to the gods by the Romans - and the incident never quite sat well with Roman writers, who tended to gloss over it with obvious discomfort.