Avellino was founded by the Irpini, the original nucleus of the city, Abellinum, was formed on the Civita hill, where numerous archaeological finds have been found, in the territory of today's Atripalda about 4 km from the center of Avellino. Archaeological evidence attest to the presence on Civita of an important pre-Roman center, presumably of Etruscan-Campanian origin and of Oscan language, dating back to at least the 4th century. According to recent research, supported by Edward Togo Salmon, the ancient city was at the center of the Sabatini territory, a Sabello people documented by Tito Livio. It is not excluded that this center had the name of Velecha, attested by numerous coins attributed to the Campania area. It was conquered by the Romans in 293 BC, who took it away from the dominion of the Irpini in the bloody battle of Aquilonia, during the Samnite Wars that took place between 343 BC. and 292 BC Under the dominion of Rome the city changed its name several times (in order: Veneria, Livia, Augusta, Alexandriana and Abellinatium). The geographical position facilitated the birth of the first settlements: since ancient times, the Sabato valley has been a natural route between Irpinia and Sannio. In 89 BC Silla occupied Pompeii, Herculaneum, Stabia, Eclano, Abella and Abellinum.

Abellinum was not yet a real urban center. It was Silla's troops who started building a real city. The Cardo and the Decumano, typical Roman urban elements, divided it into four squares, each of which led to the four external doors. The Roman city had an important development in the Augustan age, thanks to the construction of the Roman aqueduct of Serino which from the sources of Serino reached Bacoli, where the large reservoir for the supply of the Roman fleet (today called Piscina Mirabilis) was located, after serving the main cities of Campania. Abellinum assumed particular importance in the Christian age, during which the figure of the great bishop Sabino emerges, probably lived between the end of the fifth and the beginning of the sixth century. The center is documented until the mid-sixth century, thanks to the important epigraphic heritage found in the eighties-nineties in the early Christian basilica of Capo La Torre (historic center of today's Atripalda). Probably the ancient center on the Civita hill ceased to exist following the Gothic wars and the subsequent Byzantine occupation. The population dispersed on the surrounding hills, giving rise to various small new centers, including, in a still uncertain period, the new Avellino, on the Terra hill, 4 km west from Civita.

After the Lombards determined the flight of part (minority thesis) or of all (prevailing thesis) the inhabitants of Abellinum, they dispersed over the surrounding territory. Part of them began to aggregate on the Selleczanum hill, now known as Terra, originating the new city of Avellino on a tuff spur. For centuries "intra civitatem" and "intra moenia" coincided, since the city of Avellino, at the time a small village, was included within the narrow space on top of the tufaceous hill. This is because invasions, earthquakes and plagues severely slowed population growth.

Avellino was part of the Principality of Benevento until 849, to become part of the Principality of Salerno after the partition, while remaining linked to Benevento under the ecclesiastical profile, being the diocese of Avellino still a suffragan of the archdiocese of Benevento. The arrival of the Normans placed Avellino at the center of important events: in 1137 Innocenzo II and Lotario III appointed Rainulfo di Alife, the count of Avellino, Duke of Puglia, for his contribution to stop the first attempts to conquer the newly elected (1130) King of Sicily Roger II. Two years later, however, following the sudden death of Rainulfo, with the city left without the support of the Pope and Emperor, Roger II reunified the Kingdom of Sicily, annexing the Duchy of Puglia and the Principality of Capua. In the following decades, the city passed to Count Riccardo dell'Aquila, then to the Paris, the Sanseverinos, Simone di Montfort, the del Balzo, and the Filangieri de Candida. From 1287 to 1581 it was the capital of the Principatus ultra serras Montorii.

In 1512 Maria de Cardona became Countess of Avellino, who is the largest female figure in the history of the city. Under his leadership Avellino became one of the most important cultural centers of the kingdom and was able to draw as many advantages as possible from the strategic position of the city in the connections between Puglia and Naples and between Benevento and Salerno, managing to return Avellino to a thriving commercial crossroads. since after the fall of the Roman city. In order to develop the city economy and its businesses, the countess, with the help of her husband Francesco d'Este and with the well-being of his majesty Charles V, instituted the free market day, obtained permission to create a annual fair, built two ironworks in the county and started a building and administrative reorganization program, in fact a precursor of a municipal council (called order of deputies) was formed in 1548 and the office of mayor appeared for the first time; these reforms then prepared the advent of the Caracciolo dynasty towards the end of the century. The most evident result of the far-sighted guidance of the Countess de Cardona is the demographic boom which the city underwent, which went from 1000 inhabitants in 1532 to 1600 inhabitants in 1561, two years before her death.

With the abolition of feudalism, in 1806 the provincial capital of the Principality was brought back from nearby Montefusco to Avellino. The city was one of the headquarters of the riots of 1820-1821. The spread, in March 1820, also in the Kingdom of Naples, of the conquest of the constitutional regime in Spain contributed considerably to exalt the Carbonari and Masonic circles. In Naples, the conspiracy (which never intended to overthrow the king, but only to ask for the constitution) immediately took effect and also involved some senior officers, such as the brothers Florestano and Guglielmo Pepe, Michele Morelli, head of the section of the Carboneria of Nola which was joined by Giuseppe Silvati, second lieutenant, and Luigi Minichini, a Nola priest with anarchoid ideas. On the night between 1st and 2nd July 1820, the night of San Teobaldo, patron saint of the Carbonari, Morelli and Silvati started the conspiracy by deserting with about 130 men and 20 officers. The young officer Michele Morelli, supported by his own troops, proceeded towards Avellino where General Guglielmo Pepe was waiting for him.

On 2 July, in Monteforte, he was welcomed triumphantly. The following day, Morelli, Silvati and Minichini made their entrance to Avellino. Welcomed by the city authorities, reassured that their action had no intention of overthrowing the monarchy, they proclaimed the constitution on the Spanish model. After that the insurgents passed the powers into the hands of Colonel De Concilij, chief of staff of General Pepe. This gesture of submission to the military hierarchy provoked the disappointment of Minichini who returned to Nola to incite a popular revolt. As the revolt spread to Naples, where General Guglielmo Pepe had gathered many military units, on 6 July, King Ferdinand I was forced to grant the constitution. After a few months, the powers of the Holy Alliance, gathered in congress in Ljubljana, decided on armed intervention against the revolutionaries who had proclaimed the constitution in the Kingdom of the Two Sicilies. They tried to resist, but on 7 March 1821 the constitutionalists of Naples commanded by Guglielmo Pepe, although 40,000 strong, were defeated in Rieti by the Austrian troops. On 24 March the Austrians entered Naples without encountering resistance and closed the newborn parliament. After the Unification of the Peninsula, the Italian state cut off the city from the main communication routes, preventing its development.

On 14 September 1943 around 10:55 in the morning the city was heavily bombed by the Allies in an attempt to block the retreat of the Nazi troops near the strategic iron bridge. During the Anglo-American attack more than 3,000 people lost their lives, about one in eight Avellino citizens, and Piazza del Mercato, the bishop's palace and some religious and residential buildings were severely hit.

On 23 November 1980 an earthquake of magnitude 6.9 devastated the territory of central Campania and central-northern Basilicata. Several municipalities in the province were hit and in particular the municipality of Avellino counted 82 victims and considerable damage.

Map: Avellino