From Citizendium, the Citizens' Compendium
Poseidon (mythology) : In Greek mythology, (Latin: Neptune) he was the god of the sea, and of earthquakes. He was a brother of Zeus and Hades; while Zeus lived on Mount Olympus and ruled over all the Olympians, Poseidon's territory was oceans and bays including the Mediterranean Sea. In the Iliad and particularly in the Odyssey by Homer, he was a prominent force in causing the hero Odysseus to not reach home for a long time. He played a big role in the Aeneid by Virgil as well.