Figure above:
Tetradrachm coin from Potidaea, on the Chalcidice peninsula (500-480
B.C.), showing the god Poseidon riding a horse (from a private collection).
During the Classic period, Poseidon is the god of the sea, but in more
ancient times he was a deity linked to the deep earth so that Homer
still called him “Earth-shaker” (enosíchton,
or ennosígaios) (for ex.: Iliad, VII, 445;
XIII, 43). In his quality of Poseidon Hippios, he was a god of the horses,
regarded as the creator of these animals which he gave to humankind.
Particularly in Arcadia, the god was worshiped in equine form: the horse
is associated with the subterranean world, emphasizing again Poseidon’s
aspect as “Lord of the Earth”. According to the hypothesis
of some philologists (Chantraine 1968: p.931), the name of the god could
derive from posis Das, signifying “husband of the Earth”,
indicating that he originally was a male fertility spirit abiding into
the earth (Eliade 1976: p. 289-290).
[Source: https://www.numisbids.com/n.php?p=lot&sid=278&lot=47]
Figure below:
Container for offerings (rhyton) in the shape of a horse’s
head, dating to the IV century B.C. and now in the Musée des
Beaux-Arts, Lyon, France. The horse is one of the most frequently mentioned
animals in classical mythology, where it appears as attribute of some
divinity and fellow of adventures of many heroes. The animal was an
attribute of Apollo as well as of the Sun god, Helios, whose chariot
was pulled by a pair of horses. Hades, too, the Ruler of the Underworld,
travelled on a chariot pulled by horses, with which he abducted Persephone,
making her the Queen of the Underworld. The horses were deemed to be
related to the Chthonic world and to the funerary dimension, and ì,
in the Archaic period, they were often sacrificed beside their owner’s
burial.
[Source: http://marinni.dreamwidth.org/427093.html]