Painting on pottery representing Peleus trying to hold the goddess Thetis
(V century B.C.), now in the Preussischer Kulturbesitz (Staatliche Museen),
Berlin, Germany. Thetis, a marine deity, had been destined, by Zeus’s
will, to marry a mortal. The chosen candidate was Peleus, who had to
face the refusal of the goddess, transforming herself into the shape
of various animals. Notwithstanding these difficulties, Peleus was able
to hold her, during her multiple metamorphoses, until she regained her
human form and consented to marriage. All the gods participated to the
sumptuous wedding, but one goddess, Eris the goddess of discord, who
was not invited. She caused a competition among the goddesses to decide
who was the fairest one, thus determining the background for the subsequent
events leading to the Trojan war. The main character in the epic conflict
between Greeks and Trojans was Achilles, son of Peleus and Thetis.
In this case too, it can be emphasized the particular link between the
water divinities and the capacity to change shape: Nereus, for example,
who was frequently called the “Old Man of the Sea”, could
manifest himself under several aspects, while Proteus as well, another
marine divinity, was able to assume the shape of every animal. This
capacity of transformation has to be put in relationship with the fluid
nature, shapeless and mobile, of the aquatic element, which is often
regarded as the original matter of the cosmos. Moreover, the fact that
water is an indispensable ingredient for every form of life renders
it the most apt to represent the fertilizing and regenerating power
for excellence (Rudhardt 1981).
[Source: http://www.lordkat.com/blog/3356/079-quest-golden-fleece-assembling-crew-and-construction-argo.html]