Metope from the Temple E of Selinunte (470-460 B.C.), representing the
marriage between Zeus and Hera, now in the Archaeological Museum (Museo
Archeologico Regionale “Antonio Salinas”), Palermo, Italy.
Zeus was at the same time Hera’s brother and husband, and both
were born from the union of Cronus with Rhea. According to some versions,
the first sexual intercourse between Zeus and Hera occurred on the Kokkygion
Mount (the “Mountain of the Cuckoo”), in Argolis, where
Zeus had taken the aspect of a cuckoo bird. This bird, which was regarded
by the Greeks as a herald of springtime, was sacred to Hera and appears
sometimes on the scepter of the goddess. The region of Argolis was particularly
sacred to the goddess, and here were located her main centers of worship.
The intercourse between the Ruler of the gods, whose attributes are
associated with the sky powers, and his wife, who assumes some of the
aspects of the earth goddess, takes the form of a sacred marriage (hieros
gamos), between the two main cosmic powers. The temples of Zeus and
Hera at Olympia, indeed, bend one towards the other, as to indicate
the sacred intercourse between the two deities (Ferguson 1989, p. 39).
[Source: http://it.wikipedia.org/wiki/Selinunte]