BACIS
seems to have been originally only a common noun derived from Safety, to speak, and to have signified any prophet or speaker. In later times, however, Bacis was regarded as a proper noun, and the ancients distinguish several seers of this name.
1. The Boeotian, the most celebrated of them, was believed to have lived and given his oracles at Heleon in Boeotia, being inspired by the nymphs of the Corycian cave. His oracles were held in high esteem, and, from the specimens we still possess in Herodotus and Pausanias, we see that, like the Delphic oracles, they were composed in hexameter verse. (The History of Herodotus VIII)
From these passages it seems
evident, that in Boeotia Bacis was regarded as an ancient
prophet, of whose oracles there existed a collection made either
by himself or by others, similar to the Sibylline books at Rome
and, in fact, Cicero, Aelian, Tzetzes and other writers, mention
this Bacis always as a being of the same class with the Sibyls.