It was governed by a military commander (dux), and rapidly became a de facto independent state, lasting more than five centuries during the Early and High Middle Ages.

Already during the reign of the imperially appointed John I (711- ca 719), the papacy had come to the duke's aid against the Lombards, while Byzantine assistance seemed remote.

Stephen II's reign is considered a period of transition in the history of Naples: it moved away from the iconoclastic East and towards the papal West.

In 813, when Leo V the Armenian called for the fleet of the entire ducatus to aid the Byzantine admiral in combating the Saracen pirates preying on Sicily, Duke Anthimus could ignore the order; only Amalfi and Gaeta responded with contingents.

In this age, the city was mainly a military centre, ruled by an aristocracy of warriors and landowners, even though it had been compelled to surrender to the neighbouring Lombards much of its inland territory.

Anyway, Naples did not hesitate to ally with infidels if this turned to its advantage: in 836, for example, it asked for support from the Saracens in order to push off the siege of Lombard troops coming from the neighbouring Duchy of Benevento.

In 1027, duke Sergius IV donated the county of Aversa to a band of Norman mercenaries led by Rainulf Drengot, whose support he had needed in the war with the principality of Capua.