Plutarch, Theseus
Bernadotte Perrin, Ed.

Theseus was already fifty years old, according to Hellanicus, when he took part in the rape of Helen, who was not of marriageable age. Wherefore some writers, thinking to correct this heaviest accusation against him, say that he did not carry off Helen himself, but that when Idas and Lynceus had carried her off he received her in charge and watched over her and would not surrender her to the Dioscuri¹ when they demanded her; or, if you will believe it, that her own father, Tyndareus, entrusted her to Theseus, for fear of Enarsphorus, the son of Hippocoon, who sought to take Helen by force while she was yet a child. But the most probable account, and that which has the most witnesses in its favour, is as follows. [2]

Theseus and Peirithous went to Sparta in company, seized the girl as she was dancing in the temple of Artemis Orthia, and fled away with her. Their pursuers followed them no farther than Tegea, and so the two friends, when they had passed through Peloponnesus and were out of danger, made a compact with one another that the one on whom the lot fell should have Helen to wife, but should assist the other in getting another wife. [3] With this mutual understanding they cast lots, and Theseus won, and taking the maiden, who was not yet ripe for marriage, conveyed her to Aphidnae. Here he made his mother a companion of the girl, and committed both to Aphidnus, a friend of his, with strict orders to guard them in complete secrecy. [4] Then he himself, to return the service of Peirithous,journeyed with him to Epirus, in quest of the daughter of Aidoneus the king of the Molossians. This man called his wife Phersephone, his daughter Cora, and his dog Cerberus, with which beast he ordered that all suitors of his daughter should fight, promising her to him that should overcome it. However, when he learned that Peirithous and his friend were come not to woo, but to steal away his daughter, he seized them both. Peirithous he put out of the way at once by means of the dog, but Theseus he kept in close confinement.