Proper noun
Duchy of Naples
(historical) A mediaeval duchy in southern Italy, established in the 7th century CE as the Byzantine outpost Ducatus Neapolitanus; especially from 661, when Emperor Constans II appointed Basil I of Naples as the new dux (“military commander”).
The "dukes" of the Duchy of Naples were initially military commanders, called "dux" or "magister militum", appointed by the Byzantine emperor; the emperor retained interest until the 9th century, when Sergius I was elected by citizens and subsequently made his position hereditary.