Even if we'd argue that the Republic was an empire before it was the Empire (which we probably should for other reasons), Rome probably at the earliest became a

Even if we'd argue that the Republic was an empire before it was the Empire (which we probably should for other reasons), Rome probably at the earliest became an empire in the 300s BCE (and that is probably stretching it), and probably stretched to the 400s CE (if we ignore the eastern half). But even by that count, around 1 CE would at best be the "middle Roman Empire", hardly late by any calculation.