Diocletian introduced eastern-style supplication to the office of Emperor — supplicants had to be face down on the floor with their hands up, oddly enough the same way priests are ordained by the Popes. And he compelled his colleague in the w empire to retire at the same time, in order to test his system of succession. That retirement villa is (because it still stands) a fortress, and had soup-to-nuts facilities — he may have been the first survivalist. He was right near the border between the empires in case he had to raise an army and settle things down again. Mind-boggling that, until he came along, the Empire never had a fixed, orderly system of succession.
Actually, the Republic had a form of succession with two Tribunes. The Empire didn’t.