gradually usurped.

Lucan mentions a god Esus, who is represented on a Paris altar as a
woodman cutting down a tree, the branches of which are carried round to
the next side of the altar, on which is represented a bull with three
cranes--Tarvos Trigaranos. The same figure, unnamed, occurs on another
altar at Treves, but in this case the bull's head appears in the
branches, and on them sit the birds. M. Reinach applies one formula to
the subjects of these altars--"The divine Woodman hews the Tree of the
Bull with Three Cranes."[110] The whole represents some myth unknown to
us, but M. D'Arbois finds in it some allusion to events in the
Cuchulainn saga. To this we shall return.[111] Bull and tree are perhaps
both divine, and if the animal, like the images of the divine bull, is
three-horned, then the three cranes (_garanus_, "crane") may be a rebus
for three-horned (_trikeras_), or more probably three-headed
(_trikarenos_).[112] In this case woodman, tree, and bull might all be
representatives of a god of vegetation. In early 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 t