The Age of Anxiety

In less than one hundred fifty years, in fact the Empire changed its character, coming to the establishment of the Tetrarchy, the loss of the role of the capital city of Rome and the  organization of the Italian territory, which was subdivided into dioceses that were equated to the rest of the Empire. 

Ancient historians reflect on these profound changes in their world, as one can read in Cassius Dio's books, who at the beginning of the third century AD referred to the end of the reign of Marcus Aurelius as the end of the golden age: After his death, history descends from a kingdom of gold to one of iron and rust.
The decisive factor was the end of dynastic transmission of political power, which was subsequently concentrated in the hands of the army, capable of imposing the emperors and eliminate them.
It is a world that permanently changes its social structure, with the collapse of its institutions and the emergence of new social forces.