Circle of Blood, a lurid tale of a coven of baby-sacrificing witches in the catacombs of the Vatican City, released to little fanfare at the height of the Giallo craze in 1970s Italy; Luca Vozza’s only, now-lost movie eclipsed by contemporaries Mario Bava and Dario Argento. Yet it acquired a cult reputation, not only for its graphic depictions of torture and murder, but also because, it was rumoured, that some of the rites depicted were real…