A prince-bishop is a bishop who is also the civil ruler of some secular principality and sovereignty. Thus the principality or prince-bishopric ruled politically by a prince-bishop could wholly or largely overlap with his diocesan jurisdiction, but some parts of his diocese, even the city of his residence, could be exempt from his civil rule, obtaining the status of free imperial city. If the episcopal see is an archbishop, the correct term is prince-archbishop; the equivalent in the regular (monastic) clergy is prince-abbot. A prince-bishop is usually considered an elected monarch.
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In the West, with the decline of imperial power from the 4th century onwards in the face of the barbarian invasions, sometimes Christian bishops of cities took the place of the Roman commander, made secular decisions for the city and led their own troops when necessary. Later relations between a prince-bishop and the burghers were invariably not cordial. As cities demanded charters from emperors, kings, or their prince-bishops and declared themselves independent of the secular territorial magnates, friction intensified between burghers and bishops.
In the Byzantine Empire, the still autocratic Emperors passed general legal measures assigning all bishops certain rights and duties in the secular administration of their dioceses, possibly as part of a development to put the Eastern Church in the service of the Empire, with its Ecumenical Patriarch almost reduced to the Emperor's minister of religious affairs.