The curse of Oidipous upon his two sons Eteokles and Polyneikes (read the file about the Theban king Oidipous) was fulfilled. On the death of Oidipous, or in his helpless old age, or on their coming to years of discretion—the accounts vary—the two brothers could not agree which should be king; it is to be remembered that primogeniture was not a Greek institution. At length they decided to rule in alternate years, and the first year fell to Eteokles. Polyneikes, by the terms of their contract, went into banishment until his time to rule should come.
He arrived at Argos, and there fell in with Tydeus of Kalydon, who was also in banishment, for homicide. The two quarrelled, and soon came to blows, when Adrastos, son of Talaos and king of Argos, came to stop them. He had been given a mysterious oracle that he was not to allow his daughters to marry any save a lion and a boar; now Polyneikes had a lion’s skin over his shoulders, Tydeus a boar’s, or they had images of these beasts for their shield-devices. In them, therefore, Adrastos recognized the destined bridegrooms. Accordingly, Tydeus married Deipyle, daughter of Adrastos, Polyneikes her sister Argeia, to whom he gave the fatal necklace of Harmonia, which he had somehow brought with him.
Adrastos undertook to restore both his sons-in-law to their countries. Pausanias preserves a tale according to which Polyneikes left Thebes before the quarrel began, in an attempt to avoid the curse of his father, and that on that occasion he met and married Argeia; when Eteokles began to reign, he invited his brother back; the quarrel and (second) exile followed.
Eteokles had already given unequivocal signs that he was not going to yield the kingdom of Thebes to Polyneikes, or to anyone else; or it was assumed that he would not do so. In any case, no time was lost by Adrastos in getting together a large army. For leaders, besides himself and his two sons-in-law, he had Kapaneus son of Hipponoos, Hippomedon son of Aristomachos—these two were both Argives—Parthenopaios son of Meilanion and of Atalante the Arkadian huntress, and finally Amphiaraos son of Oikles, the seer. These are the Seven against Thebes.
The list is not quite agreed upon; Aeschylus includes in it Eteoklos son of Iphis, omitting Adrastos; others, according to Apollodoros, included Mekisteus and Eteoklos, omitting both Tydeus and Polyneikes, presumably as not being leaders of independent contingents.
Amphiaraos, being a seer, foreknew that the expedition would be a failure and that he, if he went on it, would never come back, indeed that no leader save Adrastos would ever return. Knowing that Polyneikes would try to enlist the persuasions of his wife, Eriphyle, he forbade her to accept any gift from that quarter. She, however, disobeyed him, was bribed with the necklace of Harmonia, and at last won her husband to join the ill-fated entcrprise. Departing reluctantly, he laid on his children the charge that they should avenge his death on their mother, and also that they should themselves make an expedition against Thebes when their time came.
Tydeus was sent to Thebes to urge the claims of Polyneikes. According to a legend as old as Homer, his mission was a stormy one, for he was waylaid on his return; Homer says it was because he had excelled all the Thebans in athletic prowess and they were jealous of him, while the later version is that it was sheer malicious treachery on the part of Eteokles, but in any case Tydeus’ single valour was too much for the fifty who attacked him from an ambush, and he killed them all, save one, whom he spared to carry home the news of what had happened to the others.
The expedition from Argos set out, and marched uneventfully as far as Nemea. Here befell the incident which led to the founding of the Nemean Games. Hypsipyle of Lemnos (read about her in the file on the Argosy) had been driven from her native island, captured by pirates, and sold as a slave to Lykurgos, king of Nemea, who had a young son, Opheltes, whose nurse she became. Adrastos’ army was short of water, or wanted running water for a sacrifice, and Hypsipyle agreed to show them a spring. She left her nursling on the ground meanwhile, and it was killed by a dragon that infested the place. Returning, the Seven found the dead child, killed the dragon, gave little Opheltes a magnificent funeral, and celebrated the games for the first time; for a considerable period, according to tradition, the Nemean Games were open only to ‘soldiers’ sons’, meaning apparently the descendants of those who served in the Argive expedition against Thebes. Hypsipyle herself was protected from the vengeance of Lykurgos and his wife Eurydike by the Argive army, and was afterwards carried away by Thoas and Euneos, her children by Jason, who after a series of adventures of no great interest had arrived at Nemea, and recognized her, with the help of Amphiaraos, according to Euripides. Amphiaraos named the dead child Opheltes Archemoros (‘Beginner of Death’), since his was the first of the many lives to be lost in the expedition.
The army now marched against the city, where after some indecisive fighting, or immediately on their arrival, they apportioned each of the seven gates of Thebes to one of their champions. According to Aeschylus, the arrangement of attack and defence was as follows:
| Gate | Assailant | Defender |
| Proitides | Tydeus | Melanippos |
| Elektrai | Kapaneus | Polyphontes |
| Neistai | Eteoklos | Megareus |
| Onkaiai | Hippomedon | Hyperbios |
| Borrhaiai | Parthenopaios | Aktor |
| Homoloides | Amphiaraos | Lasthenes |
| Hypsistai | Polyneikes | Eteokles |
However, the names in all three columns vary more or less in various authorities, for example, Euripides and Apollodoros.
The result was the utter rout of the Argives. Kapaneus, as he mounted the wall, swore that not even Zeus should keep him out of the city now, for which impiety he was struck down by a thunderbolt. Tydeus, after fighting with desperate valour, got a mortal wound. Athena, who throughout had favoured him, was minded to bring him the gift of immortality. But his ungovernable rage had got the better of him, and as she came up, she found hnn gnawing the head of Melanippos, who had also fallen. In disgust, she withheld her gift, and Tydeus died. Amphiaraos fled in his chariot, but was swallowed up alive in the earth; in later times the spot was much renowned for the true oracles which the seer continued to give after death, as in life. Adrastos escaped, thanks to the speed of his horse, Arion, offspring of Poseidon and Demeter Erinys. There remained now, for the other three (or four) assailants of the gates had also fallen, only the two brothers, Polyneikes and Eteokles; their combat ended in each killing the other. Thus was the curse of Oidipous on his two sons finally accomplished.