Exarch (Gr. leader), in the eastern Roman empire, an ecclesiastical or civil dignitary invested with extraordinary authority. At first exarchs were officers delegated by the patriarch or synod to visit a diocese for the purpose of restoring discipline. The exarch was also the superior of several monasteries, in distinction from the archimandrite, who was the superior of one, and was of a rank inferior to that of patriarch and superior to that of metropolitan. In the modern Greek church the exarch is a legate a latere of the patriarch. He visits the provinces to investigate ecclesiastical cases, the differences be-tween prelates and people, the monastic discipline, the administration of the sacraments, and the observance of the canons; and he usually succeeds to the patriarchate.-As a civil officer, the exarch was a viceroy intrusted with the administration of one or more provinces. This title was given to the prefects who from the middle of the 6th century to the middle of the 8th governed that part of Italy which was subject to the Byzantine empire. They were instituted after the reconquest of Italy from the Ostrogoths by Narses, to oppose the progress of the Lombards, then threatening to occupy that country.

They held their court at Ravenna, and combined civil, military, judicial, and often ecclesiastical authority. They appointed dukes as vice governors for several parts of Italy. The exarchate was destroyed by the Lombards in 752. When Pepin of France conquered Ravenna, it was ceded to the pope. The title of exarch for high civil and military officers remained in the West till the 12th century.