Pirithous had heard rumors about Theseus' courage and strength in battle but he wanted proof. He drove Theseus' herd of cattle from Marathon and Theseus set out to pursue him. Pirithous took up arms and the pair met, then became so impressed by each other they took oaths of friendship. He was either a son of Dia and Ixion or of Dia and Zeus.
They helped hunt the Calydonian Boar. Later, Pirithous was set to marry Hippodamia (offspring: Polypoetes). The centaurs were guests at the party, but they got drunk and tried to abduct the women, including Hippodamia. The Lapiths won the ensuing battle.
Theseus and Pirithous pledged to marry daughters of Zeus. Theseus chose Helen and together they kidnapped her when she was 13 years of age and decided to hold onto her until she was old enough to marry. Pirithous chose Persephone. They left Helen with Theseus' mother, Aethra and travelled to the underworld, domain of Persephone and her husband, Hades. Hades pretended to offer them hospitality and set a feast; as soon as the pair sat down, either snakes coiled around their feet and held them there or the stone itself grew and attached itself to their thighs.
Heracles freed Theseus but the earth shook when he attempted to liberate Pirithous. When Theseus returned to Athens, the Dioscuri, Helen's twin brothers Castor and Pollux had taken Helen and Aethra back to Sparta. Pirithous remained in Hades for eternity.
They are best known for their fight with the Lapithae, caused by their attempt to carry off Deidameia on the day of her marriage to Peirithous, king of the Lapithae, himself the son of Ixion.
Theseus, who happened to be present, assisted Peirithous, and the Centaurs were driven off (Plutarch, Theseus, 30; Ovid, Metam.
In later times they are often represented drawing the car of Dionysus, or bound and ridden by Eros, in allusion to their drunken and amorous habits.
The Centaurs are particularly celebrated in ancient story for their fight with the Lapithae, which arose at the marriage-feast of Peirithous, and the subject of which was extensively used by ancient poets and artists.
He fought against the Lapithae at the nuptials of Peirithous, and was subsequently nailed to a cross by Heracles, who is said to have made an epigram upon him, which is preserved in Philostratus.
For when Peirithous was courting Hippodameia, he gave a banquet for the Kentauroi because they were related to her; but they, unused to wine, drank too much too fast and got drunk, and when the bride was ushered in they tried to rape her.