Ammianus Marcellinus Res Gestae 26.6.14

[14] So, as had been agreed, as soon as the sun’s rays illumined the day, the aforesaid Procopius, full of conflicting emotions, went to the Anastasian Baths, named for the sister of Constantine, ¹ where he knew that the legions had their quarters. There he learned from the confidants of his secrets that their whole number in a meeting by night had united in his support. Then, after a pledge of safety was willingly given him, he was received by the throng of venal soldiers and treated indeed with honour, although he seemed in a way to be held as a prisoner; for just as once before, after the death of Pertinax, the praetorians took up Julianus, ² when he was a bidder for the imperial power, so now also these troops, with an eye to every possible gain, defended Procopius, as he plotted to enter upon his ill-starred rule.