The story of Euripides in his suppliants is disproved by Aeschylus in his Eleusinians, where Theseus himself relates the facts as here told.
The celebrated friendship between Theseus and Pirithous is said to have been thus began; the fame of the strength and valour of Theseus being spread through Greece, Pirithous was desirous to make a trial and proof of it himself, and to this end seized a herd of oxen which belonged to Theseus, and was driving them away from Marathon, and, when the news was brought that Theseus pursued him in arms, he did not fly, but turned back and went to meet him. But as soon as they had viewed one another, each so admired the gracefulness and beauty, and was seized with such respect for the courage of the other, that they forgot all thoughts of fighting; and Pirithous, first stretching out his hand to Theseus, bade him be judge in this case himself, and promised to submit willingly to any penalty he should impose. But Theseus not only forgave him all, but entreated him to be his friend and brother in arms; and they ratified their friendship by oaths.
After this Pirithous married Deidamia, and invited Theseus to the wedding, entreating him to come and see his country, and make acquaintance with the Lapithae; he had at the same time invited the Centaurs to the feast, who growing hot with wine and beginning to be insolent and wild, and offering violence to the women, the Lapithae took immediate revenge upon them, slaying many of them upon the place, and afterwards, having overcome them in battle, drove the whole race of them out of their country, Theseus all along taking their part and fighting on their side. But Herodorus gives a different relation of these things; that Theseus came not to the assistance of the Lapithae till the war was already begun; and that it was in this journey that he had his first sight of Hercules, having made it his business to find him out at Trachis, where he had chosen to rest himself after all his wanderings and his labours; and that this interview was honourably performed on each part, with extreme respect, and good-will, and admiration of each other. Yet it is more credible, as others write, that there were, before, frequent interviews between them, and that it was by the means of Theseus that Hercules was initiated at Eleusis, and purified before initiation, upon account of several rash actions of his former life.
Theseus was now fifty years old, as Hellanicus states, when he carried off Helen, who was yet too young to be married. Some writers, to take away this accusation of one of the greatest crimes laid to his charge, say, that he did not steal away Helen himself, but that Idas and Lynceus were the ravishers, who brought her to him, and committed her to his charge, and that, therefore, he refused to restore her at the demand of Castor and Pollux; or, indeed, they say her own father, Tyndarus, had sent her to be kept by him, for fear of Enarophorus, the son of Hippocoon, who would have carried her away by force when she was yet a child. But the most probable account, and that which has most witnesses on its side, is this: Theseus and Pirithous went both together to Sparta, and, having seized the young lady as she was dancing in the temple Diana Orthia, fled away with her. There were presently men sent in arms to pursue, but they followed no further than to Tegea; and Theseus and Pirithous, being now out of danger, having passed through Peloponnesus, made an agreement between themselves, that he to whom the lot should fall should have Helen to his wife, but should be obliged to assist in procuring another for his friend. The lot fell upon Theseus, who conveyed her to Aphidnae, not being yet marriageable, and delivered her to one of his allies, called Aphidnus, and, having sent his mother, Aethra, after to take care of her, desired him to keep them so secretly, that none might know where they were; which done, to return the same service to his friend Pirithous, he accompanied him in his journey to Epirus, in order to steal away the king of the Molossians' daughter. The king, his own name being Aidoneus, or Pluto, called his wife Proserpina, and his daughter Cora, and a great dog, which he kept, Cerberus, with whom he ordered all that came as suitors to his daughter to fight, and promised her to him that should overcome the beast. But having been informed that the design of Pirithous and his companion was not to court his daughter, but to force her away, he caused them both to be seized, and threw Pirithous to be torn in pieces by his dog, and put Theseus into prison, and kept him.