Along with Achilles and Patroclus, and Orestes and Pylades, Pirithous and the Athenian hero Theseus have one of the most famous male friendships in classical mythology. Pirithous was a Lapith prince when Theseus was the king of Athens. Before the two met, Pirithous had heard about Theseus' reputation for strength and bravery. He wanted proof of this reputation, so he drove Theseus' cattle from Marathon. As Pirithous expected, Theseus set out in armed pursuit. Pirithous, also armed, turned to meet his pursuer. However, as the men confronted each other, both were so impressed by the other's beauty and daring that they did not fight. Instead, Pirithous invited Theseus to assign punishment for the robbery. Theseus forgave the theft, and the two took oaths to forever be friends and brothers in arms.
The pair helped hunt the Calydonian boar, and they also took part in the battle between the Lapiths and the Centaurs. That famous battle occurred at the wedding of Pirithous and Hippodameia. The centaurs had attended the ceremony as guests, but after getting drunk, they attempted to carry off the bride and other Lapith women. The fight that followed was a favorite scene for classical artists, appearing on both the Parthenon and on the temple of Zeus at Olympia. The Latin poet Ovid also devotes a long passage in his Metamorphoses to describe the battle in detail.
On another occasion, Theseus and Pirithous promised that they would help each other wed daughters of Zeus. Theseus desired Helen of Sparta. She was twelve at the time, but Theseus and Pirithous carried her off to wait for the time when she would be old enough to marry. After they had succeeded in abducting Helen, Pirithous announced that he had chosen to wed Persephone, bride of Hades and Queen of the dead. Having left Helen with Theseus' mother, Aethra, they travelled to the underworld. Hades feigned hospitality and bade them to sit. As soon as they were seated, serpents coiled around them and held them fast.
When Heracles visited the Underworld to fetch Cerberus, he saw Pirithous and Theseus and took pity on them. With a great pull he freed Theseus, but the earth shook when he tried to free Pirithous. Theseus returned to Athens to discover that the Dioscuri had taken Helen and Aethra back to Sparta, but Pirithous remained fastened to the seat in Hades for eternity.
Note: The fateful seat in Hades is described differently by various authors. In Apollodorus, it is the "chair of forgetfulness" ("Lethe") which binds them with serpents. In other accounts, the stone of the seat grows into their flesh; Athenians are said to have such lean thighs because part of Theseus' thighs were torn off when Heracles pulled him free.