Αλιρροθιος
The son of Poseidon and the Nymph Euryte. Near Asclepius's spring in Athens he tried to rape Alcippe, the daughter of Ares, whom the god had fathered on Aglauros. Ares slew Halirrhotius, and Poseidon accused his son's murderer before a tribunal of the gods, which met on a hill thereafter known as the Areopagus (the hill of Ares).
Another version claimed that Halirrhotius, son of Poseidon, was outraged when Attica was allotted to Athena and denied to his father. In his anger, he tried to cut down the olive tree which the goddess had presented to Attica; but his axe flew out of his hands in miraculous fashion and chopped off his head.
{E2 DICTIONARY OF CLASSICAL MYTHOLOGY}