Livy, From the Foundation of the City 22.57.6

A shocking moment following the Roman defeat at Cannae.

interim ex fatalibus libris sacrificia aliquot extraordinaria facta; inter quae Gallus et Galla, Graecus et Graeca in foro bovario sub terram vivi demissi sunt in locum saxo consaeptum, iam ante hostiis humanis, minime Romano sacro, imbutum.

Meanwhile, in accordance with the books of Fate, a number of extraordinary sacrifices were made. Among these were a Gallic man and a Gallic woman, a Greek man and a Greek woman, who were buried alive beneath the ground in the Forum Boarium, in a place walled in with stone; even before this time it had been tinged with human blood in a rite that was barely Roman.