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Cult

The worship of Poseidon was extended all over Greece and southern Italy, but he was specially honoured in Peloponnese which is called "the residence of Poseidon" and in the Ionic cities. The significance of his cult is indicated by the names of cities like Poteidaia in the Chalkidiki peninsula and Poseidonia (Paestum), a Greek colony in Italy. Poseidion is a frequent Greek placename along coastlines and the name of a Greek colony at the Syrian coast.

In Ionia his cult was introduced by Achaean colonists from Greece in the 11th century BC. Traditionally the colonists came from Pylos where Poseidon was the principal god of the city. The god had a famous temple near the mountain Mycale. The month Poseidaon is the month of the winter-storms. The name of the month was used in Ionic territories, in Athens, in the islands of the Aegean and in the cities of Asia Minor. At Lesbos and Epidauros the month was called Poseidios. During this month Poseidon was worshipped as the "master of the sea" in a bright cult.

Poseidon was a major civic god of several cities: in Athens, he was second only to Athena in importance, while in Corinth and many cities of Ionia and Magna Graecia he was the chief god of the polis. Many fests of Poseidon included athletic competitions and horseracing.In Corinth his cult was related to the Isthmian games. In Arcadia his cult was related to the games "Hippocrateia" and at Sparta he had a temple near an Hippodrome. In Onchestos of Boeotia horseracing was a part of the athletic games in honour of the god.

Poseidon was considered a symbol of unity. The Panionia the festival of all Ionians near Mycale were celebrated in honour of Poseidon Helikonios and was the place of meeting of the Ionian League. He was the patron god of the Amphictiony of Kalaureia. At Onchestos of Boeotia he was worshipped as Poseidon Helikonios. His sanctuary became the place of meeting of the second Boeotian league. At Helike of Achaea there was the famous temple of Poseidon Helikonios, which was the place of meeting of the Achaean League.

The "master of the sea" createsclouds and storms, but he is also the protector of the sailors. He has the ability to calm the sea for a good voyage and save those who are in danger. He was worshipped with the surname "savior" as the protector of the seafarers and the fishermen. He is the "earthshaker", however he is also the protector against the earthquakes. In some cults he was worshipped as the "bringer of safety" or "protector of the house and the foundations".

The god was considered the creator of the first horse, and it was believed that he taught men the art of taming horses. He was depicted on horseback, or riding in a chariot drawn by two or four horses. He had a lot of temples in Arcadia, with the surname Hippios (of the horse) and he was also transformed into a horse to seduce Demeter.

Being the god of waters, Poseidon is related to the primeval water which encircles the earth (Oceanus), who is the father of all rivers and springs. He can create springs with the strike of his trident. He was worshipped as "ruler of the springs" and "leader of the nymphs" In Thessaly it was believed that he drained the area cutting the rocks of Tempe with his trident. In Greek folklore the horse can also create springs.

As god of the sea Poseidon was also god of fishing and especially of sea-fishing. Tuna was offered to him by the fishermen during the festal meal for the protection of the nets. Tuna and later dolphin was his attribute. He was worshipped in many islands and cities by the coast. At Corcyra a roaring bull near the sea-shore quaranteed a good fishing. The devastating storm of Poseidon is related to fishermen and they poured drink offerings to Poseidon - savior into the sea. The god of inland waters is very close to vegetation and Poseidon was worshipped in many cities as god of vegetation. Haloa in Athens was a fest of vegetation. The Protrygaia, a wine-fest seem to belong to Dionysus and Poseidon.

In several cities Poseidon was worshipped in relation to the genealogy and the phratry. At Tinos he was worshipped as a healer-god, probably a forerunner of the famous Evangelistria.

The bull is related to Poseidon mainly in Ionia. The sacrifice of a bull offered to Poseidon is mentioned by Homer in an Ionic festival. (Panionia) The sacrifices offered to Poseidon consisted of black and white bulls which were killed or thrown into the sea. Boars and rams were also used and in Argolis horses were thrown into a well as a sacrifice to him.

In his benign aspect, Poseidon was seen as creating new islands and offering calm seas. When offended or ignored, he supposedly struck the ground with his trident and caused chaotic springs, earthquakes, drownings and shipwrecks.Sailors prayed to Poseidon for a safe voyage, sometimes drowning horses as a sacrifice; in this way, according to a fragmentary papyrus, Alexander the Great paused at the Syrian seashore before the climactic battle of Issus, and resorted to prayers, "invoking Poseidon the sea-god, for whom he ordered a four-horse chariot to be cast into the waves".

According to Pausanias, Poseidon was one of the caretakers of the oracle at Delphi before Olympian Apollo took it over. Apollo and Poseidon worked closely in many realms: in colonization, for example, Delphic Apollo provided the authorization to go out and settle, while Poseidon watched over the colonists on their way, and provided the lustral water for the foundation-sacrifice. At one time Delphi belonged to him in common with Ge, but Apollo gave him the psychopompeion Kalaureia as a compensation for it.

Xenophon 's Anabasis describes a group of Spartan soldiers in 400–399 BC singing to Poseidon a paean —a kind of hymn normally sung for Apollo. Like Dionysus, who inflamed the maenads, Poseidon also caused certain forms of mental disturbance. A Hippocratic text of ca 400 BC, On the Sacred Disease says that he was blamed for certain types of epilepsy.

Poseidon is still worshipped today in modern Hellenic religion, among other Greek gods. The worship of Greek gods has been recognized by the Greek government since 2017.