What must have been the decay of population and of agriculture in the provinces, when even in Italy there was need of such strong protective efforts, which were nevertheless so slightly successful?

Pliny had seen what was the fatal canker of the Roman empire in the country as well as in the towns:  slavery or semi-slavery.

Landed property was overwhelmed with taxes, was subject to conditions which branded it with a sort of servitude, and was cultivated by a servile population, in whose hands it became almost barren.  The large holders were thus disgusted, and the small ruined or reduced to a condition more and more degraded.  Add to this state of things in the civil department a complete absence of freedom and vitality in the political; no elections, no discussion, no public responsibility; characters weakened by indolence and silence, or destroyed by despotic power, or corrupted by the intrigues of court or army.  Take a step farther; cast a glance over the moral department; no religious creeds and nothing left of even Paganism but its festivals and frivolous or shameful superstitions.  The philosophy of Greece and the old Roman manner of life had raised up, it is true, in the higher ranks of society Stoics and jurists, the former the last champions of morality and the dignity of human nature, the latter the last enlightened servants of the civil community.  But neither the doctrines of the Stoics nor the science and able reasoning of the jurists were lights and guides within the reach and for the use of the populace, who remained a prey to the vices and miseries of servitude or public disorders, oscillating between the wearisomeness of barren ignorance and the corruptiveness of a life of adventure.  All the causes of decay were at this time spreading throughout Roman society; not a single preservative or regenerative principle of national life was in any force or any esteem.

After the death of Marcus Aurelius the decay manifested and developed itself, almost without interruption, for the space of a century, the outward and visible sign of it being the disorganization and repeated falls of the government itself.  The series of emperors given to the Roman world by heirship or adoption, from Augustus to Marcus Aurelius, was succeeded by what may be termed an imperial anarchy; in the course of one hundred and thirty-two years the sceptre passed into the hands of thirty-nine sovereigns with the title of emperor (Augustus), and was clutched at by thirty-one pretenders, whom history has dubbed tyrants, without other claim than their fiery ambition and their trials of strength, supported at one time in such and such a province of the empire by certain legions or some local uprising, at another, and most frequently in Italy itself, by the Praetorian guards, who had at their disposal the name of Rome and the shadow of a senate.  There were Italians, Africans, Spaniards, Gauls, Britons, Illyrians, and Asiatics;