Ammianus Marcellinus Res Gestae 15.5.18

[18] Constantius, struck down by the weight of this unexpected mischance as by a thunderbolt of Fate, called a council at about midnight, and all the chief officials hastened to the palace. And when no one’s mind or tongue was equal to showing what ought to be done, mention in subdued tones was made of Ursicinus, as a man conspicuous for his sagacity in the art of war, and one who had been without reason provoked by serious injustice. And when he had been summoned by the master of ceremonies ¹ (which is the more honourable way) and had entered the council chamber, he was offered the purple to kiss much more graciously than ever before. Now it was the emperor Diocletian who was the first to introduce this foreign and royal form of adoration, whereas we have read that always before our emperors were saluted like the higher officials. ²