Ammianus ' conception of how to deal with foreigners is based on Vergil 's formulation of Rome 's mission (Aen. 6, 851-853).
There is evidence for how Ammianus thought the principle of « parcere subiectis et debellare superbos » ought to work (15, 8, 7), and why it sometimes failed (14, 10, 1-16 and 30, 3, 3-6).
The principle appears in Ammianus only when the fighting is over ; it is unfair to criticize Aeneas for failing to live up to it in circumstances to which it does not apply.
A comparison of the use of « superbia » and « superbus » in the « Aeneid » with their use in Ammianus leads to the conclusion that for Ammianus « superbia » is one of a constellation of concepts typical of barbarian behavior ; when this language is applied to barbarians it carries no moral blame.
Yet in Vergil there is no simple dichotomy between Trojans and Italians to match that in Ammianus between Romans and barbarians ; Aeneas stands at the cusp between a barbaric/ heroic and a more settled age.
