Before his pontificate, the bishop of Rome, though acknowledged to be the greatest man in the hierarchy, was not regarded as having any jurisdiction outside his own diocese. St Ambrose, for example, who was on the best of terms with the Pope of his day, obviously never regarded himself as in any degree subject to his authority. Gregory, owing partly to his personal qualities and partly to the prevailing anarchy, was able to assert successfully an authority which was admitted by ecclesiastics throughout the West, and even, to a lesser degree, in the East.

Bertrand Russell, History of Western Philosop…, loc. 1499