Large landed properties
"A second economic cause of the decline of Roman society was the monopolization of the land by a comparatively few persons. All the efforts that had been made by the statesmen of the later republic and by the emperors to remedy this evil and to create in the various provinces of the empire a body of free peasant proprietors, had effected very little. In the fifth century after Christ, as in the time of the Gracchi (par. 148), the great masses who turned the soil had not a clod that they could call their own. This condition of things foreboded disaster to the state. Any society in which the soil, nature's free and equal gift to all, is allowed to become the possession of a few and thereby the means of enslaving the many, must inevitably decay and perish."
Rome, Its Rise and Fall By Philip Van Ness Myers 1901