Seven Against Thebes.
When Oedipus was banished form Thebes, his sons Eteocles and Polyneices were minors, but it was agree that when they reached their majority they would share the rule of Thebes, taking the throne in turns for one year at a time. (Euripides claimed that Oedipus did not go into exile, but continued to rule Thebes with his wife and mother Jocasta and was later reviled and imprisoned by his sons.) At the end of his first allotted year Eteocles refused to relinquish the throne to his brother. Polyneices went to Argos, to the court of his father-in-law, Adrastus, and enlisted his support and that of five other Argive chieftains in his claim against Eteocles. These seven marched against Thebes: Adrastus, Polyneices, Tydeus of Calydon, Capaneus, Hippomedon, Pathenopaeus, and the seer Amphiaraus.
Arriving at Thebes, the seven warriors took up positions at each of the seven gates of the city and were met by seven Theban champions. One of the bravest, if foolhardy, of the Argives was Capaneus, a nephew of Adrastus. He scaled the walls, boasting that he would set fire to them even against the order of Zeus. Zeus accordingly sent a thunderbolt to destroy him; at his funeral his loyal wife, Evadne, leapt onto his funeral pyre.
Amphiaraus had resisted joining the expedition because he knew that he would die at Thebes, but he had been compelled to go by his wife, Eriphyle. He had therefore exacted a vow of vengeance from his sons Alcmeon and Amphilochus, which Almeon later enacted. During the battle at Thebes, Ampharaus was pursued in his chariot by a Theban defender, who was at the point of hurling a spear into his back when Zeus split the earth with a thunderbolt, opening a chasm into which Amphiaraus vanished.
Within the city, the seer Tiresias proclaimed that the sacrifice of a royal prince would save the city; Creon's son Menoeceus unhesitatingly volunteered. Finally Eteocles and Polyneices met in single combat, a battle that ended in their mutual deaths, fulfilling Oedipus' curse that their inheritance would be divided with a sword. Upon hearing the news, their mother, Jocasta, took her own life. Polyneices was denied burial by Creon, who assumed the regency of Thebes, but was given funeral rites by his sister Antigone, an act of defiance that caused her own death.
Of the seven, only Adrastus survived, escaping on his horse Arion, son of Poseidon and Demeter. He later met his death leading the Epigoni (sone of the seven) in the second expedition against Thebes.
The siege of Thebes became a prevalent subject in medieval romances. These postclassical treatments were largely based on Statius' epic, the Thebaid of ca. 70 CE.

See also Oedipus, at Colonus; Antigone, Eriphyle.