The town was Christianized around 500 AD, becoming an episcopal see. There followed the invasions of the Goths and Vandals. Subsequently Avellino became a Lombard centre, with a castle on the Terra hill. In the early Middle Ages it was part of the Duchy (later Principate) of Benevento and, after the latter’s fall, of the Principate of Salerno.
In 1100, during the Norman rule of southern Italy, it was acquired by Riccardo dell’Aquila. Later King Charles I of Anjou assigned it to the Montfort family, who were succeeded by the Del Balzo and the Filangierian of the House of Candia.
The feudal rights to Avellino were purchased in 1581 by Don Marino I Caracciolo, duke of Atripalda, of a patrician family of Naples, who was made Prince of Avellino in 1589. Avellino became the main seat of the Caracciolo. Don Marino’s son and grandson were consecutively Grand Chancellor of the Kingdom of Naples and chevaliers of the Order of the Golden Fleece. The grandson, Don Marino II (1587-1630), was the patron of Giambattista Basile, author of the Pentamerone.
In 1820 Avellino was seat of revolutionary riots. However, the Unification of Italy some fifty years later did not bring any benefit to the city, being cut off from the main railway line Naples-Benevento-Foggia, and far from the sea as well.
In 1943 the city was bombed by Allied planes in an attempt to cut off the retreat of German panzer units over the important Bridge of Ferriera.
Some ruins of the ancient Abellinum can be seen near the modern village of Atripalda, 4 km (2.5 mi) East of modern Avellino.
The Cathedral, with its Romanesque crypt, stands on the site of a rich and famous Roman villa which was built around 129 BC and abandoned after the eruption of Vesuvius and associated earthquake in 346.
There are some remains of the Lombard castle in Piazza Castello (Castle Square).