At first sight Roman society appears to be divided into water-tight compartments and to bristle with barriers between class and class. All free-born men (ingenui), whether citizens of Rome or elsewhere, were in principle in a distinct category, radically separated by their superiority of birth from the mass of slaves who were originally without rights, without guarantees, without personality, delivered over like a herd of brute beasts to the discretion of their master, and like a herd of beasts treated rather as inanimate objects than as sentient beings (res mancipi). Among the ingenui, again, there existed a profound distinction between the Roman citizen who was merely subject to the law. Finally, Roman citizens themselves were classified and their position on this ladder of rank determined by their fortunes.
      Whereas under the republic there had been equality for all citizens before the law, in the empire of the second and third centuries a legal distinction arose which divided the citizen body into two classes: the honestiores and the humiliores, also called plebeii or tenuiores. To the first class belonged Roman senators and knights with their families, soldiers, and veterans with their children, and men who held or had held municipal offices in towns and cities outside of Rome with their descendants. All other citizens belonged to the second, and unless wealth or ability brought them into public office, they remained there.
      The humiliores were subject to the most severe and humiliating punishments for infraction of the laws. They might be sent to the mines (ad metalla), thrown to the beasts in the amphitheater, or crucified. The honestiores, on the other hand, enjoyed certain privileges. In case of grave misconduct, they were spared punishment which would tend to degrade their position in the eyes of the people and generally got off with banishment, relegation, or losing their property.

Jerome Carcopino's "Daily Life in Ancient Rome" 1968), p 52.