His first adventure occurred at Epidaurus, where he met Periphetes, a son of Hephaestus, who was armed with an iron club, with which he killed all travellers. Having received from his grandfather a full description of this savage, Theseus at once recognized him, and rushing upon him with his sword, succeeded after a desperate encounter in killing him. He appropriated the club as a trophy of his victory, and proceeded on his journey without hinderance until he arrived at the Isthmus of Corinth.

Here the people warned him to beware of Sinnis the robber, who forced all travellers to bend with him one of the branches of a tall pine-tree. Having dragged it to the ground, the cruel Sinnis suddenly released his hold, whereupon the bough rebounding high up into the air, the unfortunate victim was dashed to the ground and killed. When Theseus beheld Sinnis advancing towards him he steadily awaited his approach; then seizing his powerful club, he killed the inhuman wretch with one blow.