Oedipus Rex and that deal with the story of Oedipus, "Oedipus Rex" was the second to be written. However, in terms of the chronology of events that the plays describe, it comes first, followed by "Oedipus at Colonus" and then "Antigone". Prior to the start of "Oedipus Rex", Oedipus has become the king of Thebes while unwittingly fulfilling a prophecy that he would kill his father, Laius (the previous king), and marry his mother, Jocasta (whom Oedipus took as his queen after solving the riddle of the Sphinx). The action of Sophocles' play concerns Oedipus' search for the murderer of Laius in
Oedipus and the Sphinx pass. Failure means his own death and that of the besieged Thebans. The riddle was: "What walks on four feet in the morning, two in the afternoon and three at night?". Oedipus answered: "Man: as an infant, he crawls on all fours; as an adult, he walks on two legs and; in old age, he uses a walking stick". Oedipus was the first to answer the riddle correctly and, having heard Oedipus' answer, the Sphinx was astounded and inexplicably killed herself by throwing herself into the sea. Oedipus thereby won the freedom of the Thebans, the kingdom of that city