"It was anathema to her to shelter her head under a roof by a city hearth. Dear to the deities of Erebus, she dwelt in deserted tombs, and haunted the graves from which ghosts had been expelled.
"The gods grant every horror at the first cry of her voice, dreading a second incantation. Living spirits, still in control of their bodies, she buries in the grave; or reversing the rite she brings back the dead from the tomb, their corpses escaping to life.
"She gathers the fragments of the funeral bier, and the fluttering grave-clothes turned to ash, and the cinders that reek of the corpse. And if the dead are sealed in a sarcophagus, that dries the internal moisture, absorbs the corruption of the marrow-bones, and stiffens the corpse, then she vents her anger eagerly on its limbs, thrusting her fingers deep in the eye-sockets, scooping out the solidified eyeballs in delight, gnawing the yellowed nails on withered hands. She mangles the hanged corpse, cuts the fatal noose with her teeth, scrapes at the crucified, tears at rain-beaten flesh and bones scorched by the sun. She steals nails that have pierced hands, the clotted gore and the black residues of putrefaction that oozed over all the limbs; and hangs her weight on sinews that resist her teeth.
"Often too, when a loved one is buried, the dreadful witch will hang over the body in kissing it, mutilates the head, opens the closed mouth with her teeth, bites the tip of the inert tongue in the dry mouth, infuses the cold lips with murmuring sound, and sends a wicked and arcane message down to the Stygian shades.
"Sextus Pompeius heard local tales of Erichtho, and made his way to her dwelling when night ruled the sky, at the hour in those deserted fields when the sun is in the zenith for those on the other side of earth..."
That chilling little passage is from Lucan's Pharsalia. You can read what happens when Sextus consults the witch here or here. I was put onto it by Paul Chrystal's book Miracula: Weird & Wonderful Stories of Ancient Greece & Rome, essential reading for any roleplayer or writer with an interest in the odd customs of the past.
The book comprises the most wonderfully abstruse collection of anecdotes, aphorisms, travel tales, superstitions, sexual practices, dining etiquette (especially important in the case of the Roman diplomat who describes going to dinner with Attila the Hun), parenting tips, ancient world science and medicine, conversation, humour, burial customs, and space travel -- and even in that list I've barely scratched the surface. The ancient curses alone (chapter 66) are worth the price of the book. I wholeheartedly recommend it.
