Defining Moment. There is no single, sharp dividing line between periods of the empire as there was between Republic and Empire. Nonetheless, one may identify certain trends particularly characteristic of the later Empire. This period may be said to start in the third century C.E. or even after the period of near-collapse that took up much of that century. It runs until 476, when Rome was sacked and the last emperor there, Romulus Augustulus, was deposed.

Growth of Despotism. The position of the emperor changed (though early signs of this change can be traced back almost to the beginning of the Empire). He became more distinct from his subjects, even those of high rank. Dominus (lord) became a conventional title—this term was the word for a slave's master or, later, the Christian God. Emperors also came...