Anthony Ossa-Richardson’s richly detailed The Devil’s Tabernacle: The Pagan Oracles in Early Modern Thought is mainly about the role that ancient oracles played in modern thought, but he begins with a fascinating overview of the place of oracles in the classical world and the Christian critique of pagan oracles.
From the time of Cicero, it was a truism that the oracles were growing silent, and Ossa-Richardson recounts one of the most dramatic texts on this point, from Lucan’s Pharsalia : “Appius Claudius visits Delphi to learn his own fate in the civil war. The temple has long been silence, since ‘kings feared the future, and forbade the gods to speak’ - a political explanation unique among the classical sources. At first the priestess, Phemonoe, afraid of prophesying, tries to dissuade Appius from his inquiry. Next she feigns inspiration. Appius at last compels her to enter the adyton and receive Apollo’s spirit. The resulting process is somewhere between rape and possession - ‘never did Paean invade Phoebas’ body with more force; he drive out the first and mortal mind, and ordered her breast to yield wholly to his own.’ The distracted priestess staggers and dashes through the temple like a Romantic heroine - little wonder that Shelley should borrow three lines for an epigraph - and at last utters her oracle: ‘at first from foaming mouth the madness wild flowed out, and groans and breathless murmurs loud emerged.’ Finally she rushes outside, collapses in convulsions, and dies” (22). This picture of “a frenzied Pythia . . . proved irresistible to early modern scholars who wanted to pain the oracle as demonic.”
That paragraph captures the feel of Ossa-Richardson’s book: Sharp writing, dramatic incident, impressive learning (that toss-off comment about Shelley).