Historia, VIII.3.8-9.
There were also some oracles spread around to the effect that the local god was promising the Aquileians victory. The god, whose worship is extremely popular, is called Bele[nu]s and identified with Apollo. Some of Maximinus’ soldiers said that his image appeared frequently in the sky fighting for the city. I am not sure whether the god really appeared to some of the men or whether it was their imagination. They were anxious to avoid the disgrace of being unable to resist a crowd of townsfolk that was numerically smaller, and wanted it ot appear that they had been defeated by gods and not men. The unusualness of the incident makes anything credible.
Herodian. History of the Empire, vol. 2, Books V-VIII. ed. and trans. C.R. Whittaker. Loeb Classical Library, v. Cambridge, MA: Harvard University Press, 1920.
Gaulish Paganism 