The sources which refer to Silvanus and his abortive usurpation are few and varied. They include a secular historian with a military background (Ammianus Marcellinus), a Roman emperor (Julian) and a lesser group composed of secular and ecclesiastical historians, orators and priests. Epigraphical evidence is slight. These sources are not of equal merit or value nor are they in absolute agreement. Indeed, the two major sources, Ammianus and Julian, differ substantially.