Because of the earlier line of division between the western and eastern parts of the Roman Empire, Illyria was ecclesiastically subject to Rome. Pope Innocent I had constituted the metropolitan of Thessalonica his vicar, in order to oppose the growing influence of the patriarch of Constantinople in the area. In a letter of about 446 to a successor bishop of Thessalonica, Anastasius, Leo reproached him for the way he had treated one of the metropolitan bishops subject to him; after giving various instructions about the functions entrusted to Anastasius and stressing that certain powers were reserved to the pope himself, Leo wrote: "The care of the universal Church should converge towards Peter's one seat, and nothing anywhere should be separated from its Head."Letter XIV, Leo to Anastasius, (Charles Lett Feltoe, tr.), Nicene and Post-Nicene Fathers, Second Series, Vol. 12. Edited by (Philip Schaff and Henry Wace, eds.) Buffalo, NY: Christian Literature Publishing Co., 1895
