EBC takes place during the rule of Julius Caesar, first noted Emperor of the Roman Empire around 47 BC. At this time they do not consider themselves a true empire. A Roman would be more likely to talk about the Fines Romani, which is Latin for Roman Territories, and not Imperium Romanum, which is the Latin of Roman Empire.
To put this in perspective;
73 BC: Spartacus, a former Roman soldier and gladiator fights against Rome.
49 BC: Julius Caesar crosses the Rubicon in Rome, causing the second civil war in Rome, ending in Caesar taking Dictatorship of Rome.
-Estimated EBC Time period
44 BC: Caesar was assassinated in the Roman Senate House