A very important modification of the root idea, and one which appears
to have a direct bearing on the sources of the Grail tradition, was that
by which, among certain peoples, the role of the god, his
responsibility for providing the requisite rain upon which the
fertility of the land, and the life of the folk, depended, was
combined with that of the King.

This was the case among the Celts; McCulloch, in The Religion of the
Celts, discussing the question of the early Irish geasa or taboo,
explains the geasa of the Irish kings as designed to promote the
welfare of the tribe, the making of rain and sunshine on which their
prosperity depended. "Their observance made the earth fruitful,
produced abundance and prosperity, and kept both the king and his land
from misfortune. The Kings were divinities on whom depended
fruitfulness and plenty, and who must therefore submit to obey their
'geasa.'[13]

The same idea seems to have prevailed in early Greece; Mr A. B. Cook,
in his studies on The European Sky-God, remarks that the king in early
Greece was regarded as the representative of Zeus: his duties could be
satisfactorily discharged only by a man who was perfect, and without
blemish, i.e., by a man in the prime of life, suffering from no defect
of body, or mind; he quotes in illustration the speech of Odysseus
(Od. 19. 109 ff.). "'Even as a king without blemish, who ruleth
god-fearing over many mighty men, and maintaineth justice, while the
black earth beareth wheat and barley, and the trees are laden with
fruit, and the flocks bring forth without fail, and the sea yieldeth
fish by reason of his good rule, and the folk prosper beneath him.'
The king who is without blemish has a flourishing kingdom, the king
who is maimed has a kingdom diseased like himself, thus the Spartans