According to tradition, the town was founded by Diomedes, the Greek hero . The earliest archaeological relics date to 1300 BC, evidence of the first settlements.
Histonium was one of the chief towns of the Frentani, situated on the coast of the Adriatic, about 9 km south of the promontory called Punta della Penna. The city is noticed by all the geographers among the towns of the Frentani, and we learn from the Liber Coloniarum that it received a colony, apparently under Julius Caesar. (Mela ii. 4. § 9; Plin. iii. 12. s. 17; Ptol. iii. 1. § 18; Lib. Colon. p. 260; Zumpt, de Colon. p. 307.) It did not, however, obtain the rank of a colonia, but continued to bear the title of a municipium, as we learn from inscriptions. (Orell. Inscr. 2603, 4052; Zumpt, l. c.) The same authorities prove that it must have been under the Roman Empire a flourishing and opulent municipal town; and this is further attested by existing remains, which include the vestiges of a theatre, baths, and other public edifices, besides numerous mosaics, statues, and columns of granite or marble. Hence there seems no doubt that it was at this period the chief city of the Frentani. (Romanelli, vol. iii. p. 32.) Among the numerous inscriptions which have been found there, one of the most curious records the fact of a youth named L. Valerius Pudens having at thirteen years of age borne away the prize of Latin poetry in the contests held at Rome in the temple of Jupiter Capitolinus. (Romanelli, l. c. p. 34; Orell. Inscr. 2603; Mommsen, I. R. N. 5252.) The name of Histonium is still found in the Itineraries of the fourth century (Itin. Ant. p. 314; Tab. Peut.), and it probably never ceased to exist on its present site, though ravaged successively by the Goths, the Lombards, the Franks, and the Arabs. Some local writers have referred to Histonium the strange passage of Strabo (vi. p. 242), in which he speaks of a place called Ortonium (as the name stands in the manuscripts) as the resort of pirates of a very wild and uncivilised character. The passage is equally inapplicable to Histonium and to Ortona, both of which names naturally suggest themselves; and Kramer is disposed to reject it altogether as spurious. (Kramer, ad loc.)
Histonium has no natural port, but a mere roadstead; and it is not improbable that in the days of its prosperity it had a dependent port at the Punta della Penna, where there is good anchorage, and where Roman remains have also been found, which have been regarded, but probably erroneously, as those of Buca. The inscriptions published by a local antiquarian, as found on the same spot, are in all probability spurious. (See Mommsen, lnscr. Regn. Neap. p. 274, App. p. 30; who has collected and published all the genuine inscriptions found at Histonium.)
After the collapse of the Western Roman Empire, the city fell to the Lombards and, finally, to the Franks. In circa 1076, Histonium was renamed Guastaymonis, or the Waste of Aimone (Italian: Il Vasto d'Ammone), following raids, hence its current name.
In the 15th century the city’s urban structure was transformed by the condottiero Giacomo Caldora, who had become its lord. The Caldoras built new city walls still seen today: Torre Bassano in Piazza Rossetti, Torre Diomede in Vico Storto del Passero, Torre Diamante in Piazza Verdi and Porta Catena, with Castello Caldoresco as its primary defensive outpost.
Under the Spanish rule of southern Italy, Vasto became fief of the Marquises of d'Avalos; in the reign of Cesare Michelangelo (marquis from 1697 to 1729), Vasto reached its zenith.
Only superficially shaken by revolutionary events in 1799 (a short-lived Republic of Vasto was immediately overthrown by the sanfedista, or loyalists), the city's history was reflected in the nation's throughout the Restoration to the Unity of Italy when a liberal elite governed.
In the age of Giovanni Giolitti, Vasto changed its architectural and urban features. The historical centre was redrawn and the foundations were set for drastic alterations during 1920s and 1930s.
Despite a devastating landslide (1956) that dragged a significant part of the eastern ridge - now Via Adriatica - into the gorge below, the years following World War II witnessed industrial, urban, parties and socio-cultural development. The city also discovered its tourist vocation: besides the progressive development of its beaches, Roman-era thermal baths, mosaics, cisterns and remains of an amphitheatre were found and restored.
Vasto is the home of Harvard University's Summer Program in Abruzzo, an intensive Italian language program for Harvard students.