Poseidon was the "god of the sea," in Greek Mythology, and is often depicted as a bearded man holding a trident while being aboard a chariot that resembles a shell - being pulled by sea horses.
Poseidon was not only known for bringing violent storms at sea, he was also notorious for bringing earthquakes to the land and was touted as being one of the most powerful gods of Mount Olympus. But, his greed for additional power, ended up leading to a dispute with the goddess Athena.
Athena & Poseidon both wanted to control the city of Athens, so they had to compete...which was a competition that involved who could provide the best gift to the people of Athens.
The other gods from Mount Olympus judged the event, and later, Zeus declared Athena as the victor. Hence, the city was named Athens.
After losing the contest, Poseidon was irate, livid and enraged to the fullest. This led to the "coming of the flood." The Sea God took his mighty trident, heavily striked the sea numerous times, caused a great storm, which ended up flooding the city of Athens. After the flood waters finally, after a long period of time, subsided, the Athenians repaired their city and built a temple - to represent Athena. They also made offerings to Poseidon, to appease the Sea God they recently disgruntled and/or enraged to fury. Temples to Poseidon at Sounion, could be seen from far out at sea. 2 rows of columns, still stand today......
---Other (less powerful deities) Sea Gods the greeks worshipped: Triton (half fish/half man), Proteus (wise, ancient one of the sea), and Glaucus.