AGATHYRNA, or AGATHYRNUM, AGATHYRSA, or AGATHYRUM, in Ancient Geography, a town of Sicily; now St Marco; as old as the war of Troy, being built by Agathyrnus, son of Æolus, on an eminence. The gentilicious name is Agathyrnæus; or, according to the Roman idiom, Agathyrnensis.