Theseus and Sinis > Basics on Sinis
Sinis is thought to have lived on the Isthmus of Corinth by the cliffs of Sceiron (Sciron).
"[E.1.2] Fourth, he [Theseus] slew Sciron, the Corinthian, son of Pelops, or, as some say, of Poseidon. He in the Megarian territory held the rocks called after him Scironian, and compelled passers-by to wash his feet, and in the act of washing he kicked them into the deep to be the prey of a huge turtle. [E.1.3] But Theseus seized him by the feet and threw him into the sea."He may have been related to the royal house of Corinth and possibly that of Troezen, as well. That would make him a blood relative of Theseus. Bacchylides calls Sinis a son of Poseidon, who was also the divine father of Theseus.
Sinis' claim to fame and Theseus' attention comes from the way in which he tortured and killed passers-by. He asked them to help him bend down a particular pine tree, but as soon as the pine neared the ground, Sinis would use its momentum to kill the helper. He'd attach the victim to the branch and let the tree reassert itself, tossing the victim to his death.
When Theseus approached, Sinis asked for the customary help, but instead of having the opportunity to kill his helper, his helper killed him, using the method Sinis had used on so many others.
"[3.16.1] Aethra bore to Aegeus a son Theseus, and when he was grown up, he pushed away the rock and took up the sandals and the sword, and hastened on foot to Athens. And he cleared the road, which had been beset by evildoers. For first in Epidaurus he slew Periphetes, son of Hephaestus and Anticlia, who was surnamed the Clubman from the club which he carried. For being crazy on his legs he carried an iron club, with which he despatched the passers-by. That club Theseus wrested from him and continued to carry about.
[3.16.2] Second, he killed Sinis, son of Polypemon and Sylea, daughter of Corinthus. This Sinis was surnamed the Pine-bender; for inhabiting the Isthmus of Corinth he used to force the passersby to keep bending pine trees; but they were too weak to do so, and being tossed up by the trees they perished miserably. In that way also Theseus killed Sinis."
"Passing on further towards the Isthmus of Peloponnesus, he slew Sinnis, often surnamed the Bender of Pines, after the same manner in which he himself had destroyed many others before. And this he did without having either practiced or ever learnt the art of bending these trees, to show that natural strength is above all art. This Sinnis had a daughter of remarkable beauty and stature, called Perigune, who, when her father was killed, fled, and was sought after everywhere by Theseus; and coming into a place overgrown with brushwood shrubs, and asparagus-thorn, there, in a childlike, innocent manner, prayed and begged them, as if they understood her, to give her shelter, with vows that if she escaped she would never cut them down nor burn them. But Theseus calling upon her, and giving her his promise that he would use her with respect, and offer her no injury, she came forth, and in due time bore him a son, named Melanippus; but afterwards was married to Deioneus, the son of Eurytus, the Oechalian, Theseus himself giving her to him. Ioxus, the son of this Melanippus who was born to Theseus, accompanied Ornytus in the colony that he carried with him into Caria, whence it is a family usage amongst the people called Ioxids, both male and female, never to burn either shrubs or asparagus-thorn, but to respect and honor them."
Plutarch Life of Theseus