Poseidon, in Greek religion and mythology, god of the sea, protector of all waters. After the fall of the Titans, Poseidon was allotted the sea. He was worshiped especially in connection with navigation; but as the god of fresh waters he also was worshiped as a fertility god. In Thessaly and other areas he was important as Hippios, god of horses, and was the father of Pegasus. Poseidon was represented as extremely powerful, with a violent and vengeful disposition. He carried the trident, with which he could split boulders and cause earthquakes. When Laomedon failed to pay him for building the walls of Troy, Poseidon sent a sea monster to ravage the Troad and years later vengefully assisted the Greeks in the Trojan War. His grudge against Odysseus is one of the themes of the Odyssey. He was the husband of Amphitrite, who bore him Triton, and by others he fathered many more sons, who usually turned out to be strong, brutal men (like Orion) or monsters (like Polyphemus). The Romans identified him with Neptune.

Greek god of water and the sea, son of Cronus and Rhea. His brothers were Zeus and Hades. When the three brothers deposed their father, the kingdom of the sea fell by lot to Poseidon. Unpredictable and sometimes violent, he was also god of earthquakes, and he was closely associated with horses. Most of his offspring were giants and savage creatures. By Medusa he was the father of the winged horse Pegasus. The Isthmian Games were held in his honor. In art he was often shown holding a trident and accompanied by a dolphin and tuna. The Romans identified him with Neptune.

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