According to history, Magellan was the first to circumnavigate the earth in 1519, however, ancient civilisations like the Phoenicians and Minoans established viable trade routes before the terms import and export were used. To explain the turbulent seas and its myriad of creatures, these same people created stories of gods who controlled the oceans and gave names to dangers a mariner faced sailing.

NASA website

Louvre
In Greek mythology, Poseidon was the god of the sea, rivers, flood and drought, earthquakes and horses. After Zeus, he was perhaps the most powerful of Olympian Gods and revered throughout the Ancient Greek world. For the city of Corinth and many cities in Magna Graecia (Greek cities along the southern coast of Italy) he was their patron god. His worship goes back to the Mycenaean period and was more important than Zeus. Linear B tablets uncovered at Mycenaean palaces, and those found at Pylos have his name written alongside Demeter and Persephone. Even in Homer’s Odyssey, Poseidon has a pivotal role in the story rather than Zeus.
How did he become god of horses? It dates back to the influences of the Indo-Europeans (Anatolia, the Aegean, Western Europe, Central Asia and southern Siberia). Some historians believe he was an aristocratic horse god and then integrated with Near Eastern aquatic deities when the Greek livelihood shifted from the land to the sea. In some images he depicted with hippocamps, a variation of sea horses.
Like his fellow Olympians, Poseidon showed many behavioural characteristics. He can be likeable in one instance and then vengeful in the next. For

circa 540 BC
Amphora
example, in the Odyssey he showed his wrath at Odysseus for blinding his son Polyphemos, but Poseidon was also angry at Odysseus who failed to offer a sacrifice when the God of the Sea prevented the Greeks from being discovered inside the Trojan Horse. It took Odysseus 10 years to finally get home as a result. He was also competitive as shown when he and Athene vied to be patron god of Athens.
Like Zeus, he had many escorts mortal and immortal, male and female. Poseidon fell in love with Pelops, which the Peloponnese is named after, and made him his lover. In another myth he pursued Demeter, who spurned him and turned herself into a mare to hide in a flock of horses. Poseidon transformed into a stallion, captured her and from their union, Arion was born—a horse capable of speech.
Poseidon and Zeus are quite similar in nature and in power yet like the ancient goddesses, his status was overturned and changed with the introduction of the new gods.
To read more go to Greek Mythology and Theoi Greek Mythology
As always, I look forward to your comments.
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References:
10 Surprising Facts About Magellan’s Circumnavigation of the Globe by Evan Andrews, History.com
Poseidon, Hellenica World
This was a very interesting post on Poseidon. I never realized his association with horses. I look forward to your next posts.
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Quite an old association at that!
Thanks Linnea 😀
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I always wondered how the horse fit in with a sea god. Now, I understand. 🙂 I’m always learning something new about Greek history from you!
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Thank you very much for the compliment 😀
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