The Sphinx's Riddle

Oedipus learned he might be a foundling and consulted an oracle, which repeated the terrible prophecy. Horrified, he left Corinth forever to protect those he thought were his parents. At a crossroads, he killed an old man (unknowingly his real father Laius) in a quarrel. He then came to Thebes, where the Sphinx was killing travelers who couldn't answer its riddle. The riddle: "What walks on four legs in morning, two at noon, three at night?" Oedipus answered "Man" and forced the Sphinx to its death.