Liber Pontificalis
(cited by Gibbon, Decline and Fall XLIX)
“Therefore, the pious man, looking back upon the profane order of that prince, armed himself against the emperor as if against an enemy, rejecting his heresy, writing to take care of the Christians everywhere, because such an impiety had arisen. The people of Pentapolis were all moved, and the armies of the Venetians resisted the order of the emperor, saying that they would never descend to the murder of the pope, but would fight in a manly fashion in his defense.”
Respiciens ergo pius vir profanam principis jussionem, jam contra Imperatorem quasi contra hostem se armavit, renuens haeresim ejus, scribens ubique se cavere Christianos, eo quod orta fuisset impietas talis. Igitur permoti omnes Pentapolenses, atque Venetiarum exercitus contra Imperatoris jussionem restiterunt; dicentes se nunquam in ejusdem pontificis condescendere necem, sed pro ejus magis defensione viriliter decertare
