Ad Nationes by Tertullian
Chapter XVII. --The Christian Refusal to Swear by the Genius of Cæsar Flippancy and Irreverence Retorted on the Heathen.
As to your charges of obstinacy and presumption, whatever you allege against us, even in these respects, there are not wanting points in which you will bear a comparison with us. Our first step in this contumacious conduct concerns that which is ranked by you immediately after the worship due to God, that is, the worship due to the majesty of the Cæsars, in respect of which we are charged with being irreligious towards them, since we neither propitiate their images nor swear by their genius. We are called enemies of the people. Well, be it so; yet at the same time (it must not be forgotten, that) the emperors find enemies amongst you heathen, and are constantly getting surnames to signalize their triumphs -- one becoming Parthicus, and another Medicus and Germanicus. On this head the Roman people must see to it who they are amongst whom there still remain nations which are unsubdued and foreign to their rule. But, at all events, you are of us, and yet you conspire against us. (In reply, we need only state) a well-known fact, that we acknowledge the fealty of Romans to the emperors. No conspiracy has ever broken out from our body: no Cæsar's blood has ever fixed a stain upon us, in the senate or even in the palace; no assumption of the purple has ever in any of the provinces been affected by us. The Syrias still exhale the odours of their corpses; still do the Gauls fail to wash away (their blood) in the waters of their Rhone. Your allegations of our insanity I omit, because they do not compromise the Roman name. But I will grapple with the charge of sacrilegious vanity, and remind you of the irreverence of your own lower classes, and the scandalous lampoons of which the statues are so cognizant, and the sneers which are sometimes uttered at the public games, and the curses with which the circus resounds. If not in arms, you are in tongue at all events always rebellious. But I suppose it is quite another affair to refuse to swear by the genius of Cæsar? For it is fairly open to doubt as to who are perjurers on this point, when you do not swear honestly even by your gods. Well, we do not call the emperor God; for on this point sannam facimus, as the saying is. But the truth is, that you who call Cæsar God both mock him, by calling him what he is not, and curse him, because he does not want to be what you call him. For he prefers living to being made a god.