The first settlements in the area date from the 7th century BC, belonging to the Apuli Italic tribe. The original nucleus of Montescaglioso grew substantially in the following centuries, thanks to trade with the nearby Greek town of Metaponto. When the latter decayed in Roman times, Montescaglioso further increased in importance. Archaeological findings include a large tuff wall dating from the 3rd century BC.

After the decline of the Western Roman Empire, Montescaglioso is mentioned first only in early medieval times. A Byzantine stronghold, it was captured by the Normans after the year 1000, and housed an important Benedictine community. Under the Angevin and Aragonese dynasties of the Kingdom of Naples, it belonged in sequence to the D'Avalos, Orsini, Loffredo, Grillo and Cattaneo feudal families.

The Benedictine Territorial Abbey (i.e. exerting diocesan authority over itself and the surrounding territory, instead of resorting under a bishop) of San Michele Arcangelo, exists at least from 1078 and was probably built in the 5th century. The Norman lord Humphrey of Hauteville and his son Rudolph made large donations to the abbey, which flourished until the 15th century. Afterwards it decayed due to numerous wars ravaging the country in those years. The Abbey Church (12th century), dedicated to St. Michael, has a notable portal and a Norman-style bell tower with mullioned windows. Renewed starting from 1590, it received a cylindrical cupola in 1650.

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