ritual, human, animal, or arboreal representatives of the god were periodically destroyed to ensure fertility, but when the god became separated from these representatives, the destruction or slaying was regarded as a sacrifice to the god, and myths arose telling how he had once slain the animal.  In this case, tree and bull, really identical, would be mythically regarded as destroyed by the god whom they had once represented.  If Esus was a god of vegetation, once represented by a tree, this would explain why, as the scholiast on Lucan relates, human sacrifices to Esus were suspended from a tree.  Esus was worshipped at Paris and at Treves; a coin with the name AEsus was found in England; and personal names like Esugenos, “son of Esus,” and Esunertus, “he who has the strength of Esus,” occur in England, France, and Switzerland.[113] Thus the cult of this god may have been comparatively widespread.  But there is no evidence that he was a Celtic Jehovah or a member, with Teutates and Taranis, of a pan-Celtic triad, or that this triad, introduced by Gauls, was not accepted by the Druids.[114] Had such a great triad existed, some instance of the occurrence of the three names on one inscription would certainly have been found.  Lucan does not refer to the gods as a triad, nor as gods of all the Celts, or even of one tribe.  He lays stress merely on the fact that they were worshipped with human sacrifice, and they were apparently more or less well-known local gods.[115]

The insular Celts believed that some of their gods lived on or in hills.  We do not know whether such a belief was entertained by the Gauls, though some of their deities were worshipped on hills, like the Puy de Dome.  There is also evidence of mountain worship among them.  One inscription runs, “To the Mountains”; a god of the Pennine Alps, Poeninus, was equated with Juppiter; and the god of the Vosges mountains was called Vosegus, perhaps still surviving in the giant supposed to haunt them.[116]

Certain grouped gods, Dii Casses, were worshipped by Celts on the right bank of the Rhine, but nothing is known regarding their functions, unless they were road gods.  The name means “beautiful” or “pleasant,” and Cassi appears in personal and tribal names, and also in Cassiterides, an early name of Britain, perhaps signifying that the new lands were “more beautiful” than those the Celts had left.  When tin was discovered in Britain, the Mediterranean traders called it [Greek:  chassiteros], after the name of the place where it was found, as cupreus, “copper,” was so called from Cyprus.[117]