Acis,
the son of the Italic god Faunus and the Nymph Symaethis, gained the love
of the Nereid, or the sea nymph, Galatea. Galatea had another admirer,
Cyclopus Polyphermus, who loved her without any hope for success. He played
for Galatea love songs on his pipes. Once he found her lying in the arms
of Acis. In his intense jealousy, Polyphermus tried to crash his rival
under rocks, but Acis turned himself into river and thus escaped from the
giant.
See: Nicolas Poussin. Acis
and Galathea.