Res Gestae

The envoys followed with no less diligence, bearing with them the messages which I have mentioned and intent upon their journey; when, however, they fell in with higher officials they were covertly detained, but after suffering continual and serious delays as they passed through Italy and Illyricum, they at last crossed the Bosporus, and proceeding by slow stages found Constantius still tarrying in Cappadocia at Caesarea. This was a well-situated and populous city, formerly called Mazaca, situated at the foot of Mount Argaeus.

When the envoys were given audience, they presented their letters, but no sooner were they read than the emperor burst out in an immoderate blaze of anger, and looking at them askance in such a way that they feared for their lives, he ordered them to get out, asking no further questions and refusing to listen to anything.