During a happy period of more than fourscore years, the public administration was conducted by the virtue and abilities of Nerva, Trajan, Hadrian, and the two Antonines.

It is the design of this, and of the two succeeding chapters, to describe the prosperous condition of their empire; and after wards, from the death of Marcus Antoninus, to deduce the most important circumstances of its decline and fall; a revolution which will ever be remembered, and is still felt by the nations of the earth.
The principal conquests of the Romans were achieved under the republic; and the emperors, for the most part, were satisfied with preserving those dominions which had been acquired by the policy of the senate, the active emulations of the consuls, and the martial enthusiasm of the people.

The seven first centuries were filled with a rapid succession of triumphs; but it was reserved for Augustus to relinquish the ambitious design of subduing the whole earth, and to introduce a spirit of moderation into the public councils.

Inclined to peace by his temper and situation, it was easy for him to discover that Rome, in her present exalted situation, had much less to hope than to fear from the chance of arms; and that, in the prosecution of remote wars, the undertaking became every day more difficult, the event more doubtful, and the possession more precarious, and less beneficial.

The experience of Augustus added weight to these salutary reflections, and effectually convinced him that, by the prudent vigor of his counsels, it would be easy to secure every concession which the safety or the dignity of Rome might require from the most formidable barbarians.