I would like to understand how Rome transformed from republic to empire from the point of view of Latin language. I think I already have a sufficient understanding of Roman history to understand the political transformation, but I realized that I know almost nothing about how this transform was described by contemporaries in Latin.
When the Roman Republic become the Roman Empire, was there any change in how Romans referred to their country? An obvious first guess is that in the republic era it was called res publica Romana and later on imperium Romanum. However, it seems likely to me that res publica simply meant "state", republic or not, and imperium meant something like "command", "realm" or "authority". In this reading res publica Romana would mean the state of Rome from a political point of view and imperium Romanum the area under Rome's control. Evolving res publica and imperium into today's concepts of "republic" and "empire" can well be a later development.
To understand this issue, I would like to know an answer to these (interwoven) questions:
- What were the Roman Republic and the Roman Empire called in classical Latin when one wanted to make a distinction? My dictionary translates "republic" and "empire" as libera res publica and imperium, respectively, but I don't think this is the whole story.
- Did the way Romans referred to their state change when the republic became an empire?
- What did res publica Romana and imperium Romanum (and perhaps senatus populusque Romanus) exactly refer to? Was their use limited to some eras?
- Is there an ancient Latin text discussing a change in the name of the state due to the republic turning into an empire?
The transition was slow: the first stages of what we today know as the empire was seen as continuation of the republic. But the Romans must have realized that their republic was not the way it used to be before the principate turned into the dominate. I would like to know how the process was reflected in references to the state in the extant literature.
To answer this question, it is not necessary to answer every single question listed above — although I would be happy to see a thorough answer. I hope the list conveys the problem I want to have cleared up. Due to the somewhat broad nature of the question I want to explicitly encourage partial answers.