>So, it's hard to say exactly when the Republic ceased and
>the Empire began. I said Augustus, but perhaps it was
>Sulla, maybe? Marcus? The Gracchi brothers (that's my bet)?
>The Republic and the Empire overlapped for a long time,
>which is probably the fairest way of putting it.
Well, formally there's a date for the big transformation, and that's the day Octavian became Augustus and, quietly, emperor in 27BC. Arguably, Julius Caesar had equivalent status back in Februray 44BC, when he was dubbed *dictator perpetuus*, but relations with both patricians and plebians were such that Julius never quite had the substantial power his formal title implied (as March 15 was to evince). Sulla's dictatorial status in 81BC seems formally no weaker than Julius's was in 44 - but then, there was a hell of a lot more empire to be dicatator of in 44. I haven't had a look at this stuff for twenty-five years (when I was absolutely besotted with it), but I doubt Tiberius Gracchus ever really had the office of emperor in mind (the Roman sources disagree about the Gracchi a lot - the republic was coming apart at the seams, and feelings were hot, which is reflected in the histories). Same with Gaius Gracchus. It just wasn't on, really - the Senate might have been a crucible of intrigue, but it had more than enough clout to outweigh all the indignation the plebians could muster.
So I reckon we can talk emperor effectively as of 81BC, formally as of 27BC, and openly as of the Senate's public pronouncement of Augustus's promotion to *imperium proconsulare maius infinitum* in 23 BC.
Cheers, Rob.