Vasto (Abruzzese: lù Uàštë; Ancient Greek: Histonion, Latin: Histonium) is a comune on the Adriatic coast of the Province of Chieti, in southern Abruzzo, Italy. During the Middle Ages it was called Guastaymonis, Vasto d'Aimone or Waste d'Aimone. Fascist Italy called the city Istonio, but it was renamed Vasto in 1944.