Abstract

At the end of book twenty of his Res Gestae Ammianus Marcellinus depicts an abundance of rainbows above the Roman army commanded by Constantius II in Persia. The significance of the rainbows as an omen is informed by his use of poetry, principally Virgil’s Aeneid. The rainbows foreshadow the death of Constantius II and the rise of Julian. Constantius’ subsequent decision to withdraw his army to winter in Antioch is framed as an anxious reaction to their presence. The episode responds to a debate contemporary with Ammianus’ own period regarding the supposed ability of Constantius and Julian to foresee events.