Used legally for the first time in the canons of the Council of Nicea (325), the term denoted the bishop of the principal city of a province. Insofar as institutional Christianity achieved a shape analogous to Roman imperial administration, and had a membership somewhat proportional to the population distribution of the empire, the centers of one served as centers of the other. The concept goes back to the first millennium b.c., by the end of which “metropolis” was applied to a major center such as Rome, or to a minor location such as Laodicea. By the sixth century, according to Evagrius, the metropolitan was under the exarch, reflecting the regrouping of provinces into dioceses; by the tenth century he ranked above other archbishops.