that the Celtic image of Zeus was a lofty oak, perhaps a rough-hewn trunk rather than a growing tree, and such roughly carved tree-trunks, images of gods, are referred to by Lucan in his description of the Massilian grove.[968] Pillar stones set up over the graves of the dead are often mentioned in Irish texts.  These would certainly be associated with the dead; indeed, existing legends show that they were believed to be tenanted by the ghosts and to have the power of motion.  This suggests that they had been regarded as images of the dead.  Other stones honoured in Ireland were the cloch labrais, an oracular stone; the lia fail, or coronation stone, which shouted when a king of the Milesian race seated himself upon it; and the lia adrada, or stone of adoration, apparently a boundary stone.[969] The plurima simulacra of the Gaulish Mercury may have been boundary stones like those dedicated to Mercury or Hermes among the Romans and Greeks.  Did Caesar conclude, or was it actually the case, that the Gauls dedicated such stones to a god of boundaries who might be equated with Mercury?  Many such standing stones still exist in France, and their number must have been greater in Caesar’s time.  Seeing them the objects of superstitious observances, he may have concluded that they were simulacra of a god.  Other Romans besides himself had been struck by the resemblance of these stones to their Hermai, and perhaps the Gauls, if they did not already regard them as symbols of a god, acquiesced in the resemblance.  Thus, on the menhir of Kervadel are sculptured four figures, one being that of Mercury, dating from Gallo-Roman times.  Beneath another, near Peronne, a bronze statuette of Mercury was discovered.[970] This would seem to show that the Gauls had a cult of pillar stones associated with a god of boundaries.  Caesar probably uses the word simulacrum in the sense of “symbol” rather than “image,” though he may have meant native images not fully carved in human shape, like the Irish cermand, cerstach, ornamented with gold and silver, the “chief idol” of north Ireland, or like the similarly ornamented “images” of Cromm Cruaich and his satellites.[971] The adoration of sacred stones continued into Christian times and was much opposed by the Church.[972] S. Samson of Dol (sixth century) found men dancing round a simulacrum abominabile, which seems to have been a kind of standing stone, and having besought them to desist, he carved a cross upon it.[973] Several menhirion in France are now similarly ornamented.[974]

The number of existing Gallo-Roman images shows that the Celts had not adopted a custom which was foreign to them, and they must have already possessed rude native images.  The disappearance of these would be explained if they were made of perishable material.  Wooden images of the Matres have been occasionally found, and these may be pre-Roman.  Some of the images of the three-headed and crouching gods show