In the Greek mythology was the sea-god Poseison one of the major gods of the Olympos as being the brother of Zeus and Hades. He created new islands and was responsible for calm seas but in his anger when offended or ignored he caused earthquakes and shipwrecks. Sailors prayed to him asking for a safe voyage sometimes offering horses which were drowned. The Romans also had a major god of the sea called Neptune (from the Etruscan Nethuns).
