4. The same conclusion results from the consideration of the absolute amount of the public revenue levied in the Roman empire, compared with what is extracted from modern states. Gibbon estimates the public revenue of the whole empire in the time of Augustus, at "fifteen or sixteen millions sterling;"[40] and in the time of Constantine the revenue derived from Gaul was £4,500,000 a-year.[41] The first of these sums is less than a _third_ of what is now levied in time of peace on Great Britain, with less than thirty millions of souls, instead of the hundred and twenty millions who swelled the population rolls of the Roman empire: the last is little more than an _eighth_ of what is now extracted from France, having nearly the same limits as ancient Gaul. Supposing that the value of money has declined, from the discovery of the South American mines, a half, (and at _this_ time, owing to the decline of those mines, it has not sunk more,) still it is apparent that the public burdens of modern times are at least three times as heavy as they were in the Roman empire in the highest period of its greatness. As its strength and military establishment constantly declined after that period, there is no reason to suppose that the absolute amount of the public taxes was at any subsequent time greater, although unquestionably, from the decline in the resources of those who were to bear them, they were felt as infinitely more oppressive. And that these taxes were not disproportioned to the strength of the empire, when its resources were unimpaired, and its industry flourishing, is decisively proved by the extremely prosperous condition in which it was during the eighty years when Nerva, Trajan, Adrian, and the two Antonines filled the imperial throne. "At that period," says Gibbon, "notwithstanding the propensity of mankind to exalt the past and depreciate the present, the tranquil and prosperous condition of the empire was warmly felt and honestly confessed by the provincials as well as the Romans."[42] "They affirm," says a contemporary writer, "that, with the increase of the arts, the human species has visibly multiplied. They celebrate the increasing beauty of the cities, the beautiful face of the country, cultivated and adorned like an immense garden, and the long festival of peace which was enjoyed by so many nations, forgetful of their ancient animosities, and delivered from the apprehension of future danger."[43]