Ammianus Marcellinus Res Gestae 21.16.11

[11] And in such affairs he showed deadly enmity to justice, although he made a special effort to be considered just and merciful. And as sparks flying from a dry forest even with a light breeze of wind come with irresistible course and bring danger to rural villages, so he also from trivial causes roused up a mass of evils, unlike that revered prince Marcus, ¹ who, when Cassius had mounted to imperial heights in Syria, and a packet of letters sent by him to his accomplices had fallen into the emperor’s hands through the capture of their bearer, at once ordered it to be burned unopened, in order that, being at the time still in Illyricum, he might not know who were plotting against him, and hence be forced to hate some men against his will. ²