In 533, the Vandal Kingdom was conquered by Byzantine forces under Justinian's general Belisarius. Caesarea was among the areas to return to imperial rule. It was the seat of Mauretania's duke (), but it went into decline and its city center was given over to ramshackle housing for the poor. The first duke was named John; that he was given an infantry unit rather than cavalry implies that he was meant to hold the port without much concern about controlling its surrounding hinterland.