The Archbishop of Mainz was an influential ecclesiastic and secular prince in the Holy Roman Empire between 780–82 and 1802. In Church hierarchy, the Archbishop of Mainz was the primas Germaniae, the substitute of the Pope north of the Alps. Aside from Rome, the See of Mainz is the only other see referred to as a "Holy See", although this usage has become rather less common.
The see was established in ancient Roman times, in the city of Mainz, which had been a Roman provincial capital called Moguntiacum, but the office really came to prominence upon its elevation to an archdiocese in 780/82. The first bishops before the 4th century have legendary names, beginning with Crescens. The first verifiable Bishop of Mainz was Martinus in 343. The ecclesiastical and secular importance of Mainz dates from the accession of St. Boniface to the see in 747. Boniface was previously an archbishop, but the honor did not immediately devolve upon the see itself until his successor Lullus.
The modern Diocese of Mainz was founded in 1802, within the territory of France and in 1814 its jurisdiction was extended over the territory of Hesse-Darmstadt. Since then it has had two cardinals and via various concordats was allowed to retain the mediæval tradition of the cathedral chapter electing a successor to the bishop.
