Lucan describes realistically the awful sacrifices of the Gauls on cruel altars not a whit milder than those of Diana, and he speaks of "altars piled with offerings" in the sacred grove at Marseilles.[965] Cicero says that human victims were sacrificed on altars, and Tacitus describes the altars of Mona smeared with human blood.[966] "Druids' altars" are mentioned in the Irish "Expedition of Dathi," and Cormac speaks of _indelba_, or altars adorned with emblems.[967] Probably many of these altars were mere heaps of stone like the Norse _horg_, or a great block of stone. Some sacrifices, however, were too extensive to be offered on an altar, but in such cases the blood would be sprinkled upon it. Under Roman influence, Celtic altars took the form of those of the conquerors, with inscriptions containing names of native or Roman gods and bas-reliefs depicting some of these. The old idea that dolmens were Celtic altars is now abandoned. They were places of sepulture of the Neolithic or early Bronze Age, and were originally covered with a mound of earth. During the era of Celtic paganism they were therefore hidden from sight, and it is only in later times that the earth has been removed and the massive stones, arranged so as to form a species of chamber, have been laid bare. IMAGES. The Gauls, according to Cæsar, possessed _plurima simulacra_ of the native Mercury, but he does not refer to images of other gods. We need not infer from this that the Celts had a prejudice against images, for among the Irish Celts images are often mentioned, and in Gaul under Roman rule many images existed.