When the “barbarians” from the East stormed the gates of Rome in the fifth century, the great capital of the empire was shaken to the core. Ignoring more obvious reasons for the collapse (e.g., economic, military, and moral corruption), some leading citizens argued vociferously that Christianity was to blame for Rome’s demise: Rome fell because the city had turned its back on the pagan gods.
Responding to these charges, Augustine of Hippo stepped into the fray by writing The City of God. The bishop from northern Africa retorted that Rome’s problem was not that it had taken Christianity too seriously, but that it had not taken Christianity seriously enough. In the passage below, Augustine observes that a virtuous emperor will be a blessed emperor. By regarding the regent as merely an agent of God and not a god himself, Augustine helped lay the foundation for the modern notion of the limitations of powers.
But we say that they are happy if they rule justly;
if they are not lifted up amid the praises of those who pay them sublime honours, and the obsequiousness of those who salute them with an excessive humility, but remember that they are men;
if they make their power the handmaid of His majesty by using it for the greatest possible extension of His worship;
if they fear, love, worship God; if more than their own they love that kingdom in which they are not afraid to have partners;
if they are slow to punish, ready to pardon; if they apply that punishment as necessary to government and defence of the republic, and not in order to gratify their own enmity;
if they grant pardon, not that iniquity may go unpunished, but with the hope that the transgressor may amend his ways;
if they compensate with the lenity of mercy and the liberality of benevolence for whatever severity they may be compelled to decree;
if their luxury is as much restrained as it might have been unrestrained;
if they prefer to govern depraved desires rather than any nation whatever; and
if they do all these things, not through ardent desire of empty glory, but through love of eternal felicity, . . .
Such Christian emperors, we say, are happy in the present time by hope, and are destined to be so in the enjoyment of the reality itself, when that which we wait for shall have arrived.
 Augustine, The City of God, trans. Marcus Dods (New York: Random House, 1950), 178. In other translations the quote can be found in Book 5, Chapter 24.