AGATHYRNA, or AGATHYRNUM, AGATHYRSA, (Polybius;) AGATHYRNUM, (Strabo;) a town of Sicily; now S. Marco; as old as the war of Troy, being built by Agathyrnus, son of Æolus, on an eminence. The gentilicious name is Agathyrnus; or, according to the Roman idiom, Agathyrmenus.