History

Poseidon was born full-growth. After his birth, he was swallowed by his own father, Cronus, because he heard of a prophecy that one of his children would overthrow him. The article, "Poseidon's Birth Story," states, "Later on, it was Zeus who avoided getting swallowed, and who got the rest of his siblings out by giving his father something to make him vomit," (Greek Boston). After this, his children came together and overthrew Cronus, as the prophecy foretold. 

"The Myth of Poseidon"