Carefully Follow The Rules

Letter 3,30 - to John, sub-deacon. April 593

"With the death, therefore, of Laurence, bishop of the church of Milan, the clergy gave notice in their report to us that they had agreed unanimously in the election of our son Constantius, their deacon. But since the same report was not signed, to prevent us from overlooking anything that concerns security, it is therefore necessary for you to set out for Genoa, supported by the authority of this command. And because many of the inhabitants of Milan have settled there, forced by barbaric savagery, you should call them together and carefully consider their wishes.
And if no discord keeps them from agreement over the election, once you find that the wishes and consensus of all stay firm concerning our son, the above-mentioned Constantius, then you can have him consecrated by the local bishops, as the ancient custom demands, with the assent of our authority and the Lord's solace.
Thus with preservation of this sort of custom, the apostolic see may both retain its proper strength and not diminish its own right by allowing others to share them.

Cited from: The Letters of Gregory the Great, trans. John R.C. Martyn (Toronto: PIMS, 2004), I: 255.