The Duchy of Naples (Latin: Ducatus Neapolitanus, Italian: Ducato di Napoli) began as a Byzantine province that was constituted in the seventh century, in the reduced coastal lands that the Lombards had not conquered during their invasion of Italy in the sixth century. 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.
Read more about Duchy Of Naples: Lombard Invasion and Neapolitan Unrest, First Local Duchy, Papal Suzerainty, Hereditary Dukeship, Struggles For Relevance in The Norman South