As changeable as the sea that he rules over, Poseidon is a moody and sometimes dark god filled with an awesome depth of power and one who places great value on tradition. Poseidon dwelt deep within the Aegean in a palace on the sea floor made of coral and gems and filled with all manner of treasures salvaged from shipwrecks. He rode upon the waves in his chariot pulled by foam-white hippocamppi (horses with the tails of fish), brandishing his trident, the three pronged fish spear, and acompanied by dolphins and okianids – the beautiful sea nymph daughters of Okeanos, an ancinet sea god. Poseidon likely started out his existence as a god of rivers and springs and fresh water, one possible source of his name is Poti-don – ‘river lord’ while another possibility is ‘husband of the distributor’ and could connect him to Demeter in early cult. Poseidon is also known as the god of earthquakes (‘Enosides’ is one of his epithets meaning earth-shaker) and a bringer of madness (he was considered to be the source of certain types of epilepsy). He is also the lord of horses; horses and the sea have a stong connection and it is not so odd that he would have dominion over both. Both horses and the sea are forms of travel, carriers of communications and sorces of food (horse meat and fishing) both transporters of colonists (Poseidon was also a patron of colonization) and in the ancient world horses and herds were and traded by ship. One of the most famous pan-hellenic games was held in his honour, the Isthmian games held in Corinth and featured horse and chariot races. Sailors would pray to Poseidon for safe travel and calm seas and would often drown a horse in supplication. Poseidon was also the guardian of navies, including the one of Athens even though the people of that city chose Athene to be their patron valuing her gift of the olive tree over his of a salt water spring. Poseidon also lost patronage of another city to a goddess when Hera won Argos as her own.
Poseidon was also known for his temper and wrath. At insult he would send great sea monsters to devastate those who offended him. The Ketos Aithiopios (the Ethiopian Sea Monster, also known as the Kraken) was sent to devastate the kingdom of king Kepheus and Queen Kassiopeia when she boasted her daughter was more beautiful than all the sea nymphs. The life of her daughter Amdromedea was the price to free them from the creature, though she was saved by the hero Perseus before being devoured. The monster Ketos Troios devastated the Trojan kingdom in much the same way when King Laomedon refused payment to Poseidon and Apollon for building the great walls of his city. Poseidon’s wrath also caused great havoc in Minos’ kingdom of Krete. Minos had prayed for a miracle to prove his right to kingship and a great white bull emerged from the sea, but instead of sacrificing it to Poseidon as promised he kept the beast for himself and the god caused the queen, Pasiphae, to fall in love with the creature and after mating with it birthed the monstrous Minotaur.
Though the son of Kronos and Rhea he was not raised by them. Kronos had swallowed his children at their birth, to prevent succession as well as to absorb the authority and power they had over the natural world. There are other stories that speak of Poseidon being cast into the sea by an angry Kronos or being hidden among a field of sheep by Rhea (who gave a foal in his place for Kronos to devour) or his fosterage among the mysterious sea deities, the Telkhines on Rhodes, much as Zeus was raised by the Korybantes on Krete. Poseidon is married to the goddess Amphitrite a nerid daughter of Nerus and Doris and by her fathered the fish tailed Triton. Another love of Poseidon was the youth Pelops, the son of Tantalus who Poseidon took up to Olympus for a time as his lover and later gave him a winged chariot with which he won the hand of the princess Hippodamia. Poseidon fathered the nymph Kharybdis who was turned into a great whirlpool, one of the most dangerous features of the ancient sea. Demeter bore children to Poseidon as well, the mysterious goddess Despoine (possibly the Arkadian variant of Persephone) and the talking stallion Arion. By Gaia, Poseidon fathered many strange giant creatures including Antaus who could not be harmed as long as part of him touched his mother (he was killed by Herakles who lifted him into the air and crushed him) and posibly the kyklopes Polyphemus who was blinded by Odyseus (which was the cause of Poseidon’s hatred of the hero). By Aphrodite Poseidon is said to have fathered Herophilus the god of the love for the sea and with the mortal princess Aethra is said to be the father of the great hero and Athenian king Theseus. There are some hints that Poseidon was also considered the father of the goddess Athene before Zeus, though this is conjecture and will likely never be known one way or the other. It was in Athene’s temple that Poseidon had one of his most famous affairs, with the beautiful priestess Medousa who was turned into a strange creature that could turn men to stone by a furious Athene. When she was decapitated by Perseus, the children conceived by her and Poseidon were finally released from her body – the giant Krysaor and the famed winged steed Pegasos. Poseidon is also said to have fathered the first of the mortal horses as well, while sleeping, his seamen fell upon a stone from which sprang the first stallion.
In those pantheons related to the Greek there are many deities who share similarities to Poseidon, the best known being the Roman Neptune, whose focus was more as a god of hoses than the sea. Nethuns is the Etruscan parallel to Poseidon and is possibly related, as well as Njordr of the Norse pantheon and Rodon in the Illyrian. There is also an Atlantean connection to Poseidon where myth tells that he was the chief god of their pantheon, he may also have been the chief god of the pre-hellenic Mykenean culture, a heavily sea-faring culture though in it there is no connection of Poseidon to the sea. He appears in Linear B under the name PO-SE-DA-O-NE and a feminine variant of his name (PO-SE-DE-JA) was also found as well as inscriptions refering to "the Two Queens and Poseidon" and "the Two Queens and the King" (the two queens likely being the early versions of Demeter and Persephone).
I honor Poseidon when I travel and ask for his protection, I may not spend much time on the sea but I do travel by car and ‘horse-power’ seems to me to be soilidly uinder his sphereof influence. I often spend time near rivers, walking or sometime canoeing and when I am lucky enough to be near large bodies of water I offer thanks to this god for the shear, overwheling beauty that they bring into the world.