ONE year after he became Rome’s first official emperor, Augustus completed a building project which his great-uncle Julius Caesar – the military dictator who polished off the limited democracy of the Republic – had started. It was, says Mary Beard in her new book Emperor of Rome: “A vast new marble voting hall.” It could hold 50,000 people.

But what need had Rome for voting? It was now under one-man-rule. So Augustus turned it into “a proto-Colosseum” to stage gladiatorial shows.

Beard’s rollickingly readable history sets out to establish just want it ‘meant’ to be an emperor. The voting hall story is an apt case-study. If there’s anything which unites Rome’s emperors it’s ruthless dictatorship, and the fact that the bloody business of hosting gladiatorial combat was key to their success. Citizens had no say, but keep them entertained and emperors had a decent chance of lasting.

Emperors were as different as prime ministers and presidents. Each had their own style, their own court and advisors, their own obsessions, strengths and weaknesses. Emperors didn’t even need to be Roman. After Domitian’s death in 96AD, Roman scholars consider all emperors “foreign”. Hadrian and Trajan were Spanish-born, Septimius Severus Libyan.

Another unifying characteristic was this: if emperors were followed onto the throne by someone they’d chosen as heir (emperors often had no sons thanks to rampant child mortality, and so adopted their preferred candidate) then they were basically guaranteed a favoured place in history. Why would a ‘chosen one’ smear their benefactor’s name? Why would someone picked by a literal ‘god’ not praise their predecessor to the heavens - especially if it sped up their own elevation to divine-status.

The Herald: Life in Rome could be brutalLife in Rome could be brutal (Image: free)

If, however, emperors were killed and some usurper took power, then their reputation would be trashed by an incomer who owed them nothing. This happened with alarming frequency. Of the first five emperors, none died naturally.

Caligula, an emperor now remembered as uniquely awful, could well have been joking when he infamously suggested making his horse a senator. The trouble is, after his assassination, this possible quip became proof of his madness.

As Beard says: “The impression we are meant to take away is that emperors were assassinated because they were monsters. It is equally likely that they were made into monsters because they were assassinated.”

After his suicide, Nero, seen as another hideous specimen, had flocks of mourners laying flowers at his tomb for years. Presumably, Beard notes, these folk “did not see him as the tyrant he is often assumed to be”.

Nevertheless, there were plenty of genuine lunatics on the throne. Enter Elagabalus, with his gift for the murderous flourish. He once used retracting ceilings and tonnes of rose petals to suffocate - so the story goes - guests who’d got on his nerves.

Tiberius - most probably a serial sex criminal - had a penchant for setting his courtiers questions on whatever subject he’d been reading about. It was all designed so he’d win every quiz. One unfortunate flunkey, who thought Tiberius might like it if he’d read the same books as the emperor, won the quiz and was promptly ordered to kill himself.

Becoming emperor also conferred paranoia. Domitian had walls lined with reflective stone so he could see assassins creeping up. Two brothers once ruled together, Geta and Caracalla. They detested each other so much they had separate entrances built to their palace so they’d never have to see one another. Eventually, Caracalla ordered his guards to kill his brother - in front of their own mother. Caracalla then subjected Geta to ‘damnatio memoriae’: condemnation of memory, which saw every reference to Geta struck from history.

As long as they kept the elites happy, and the mob content with bread and circuses, emperors could live the most extravagant lives. Hadrian, for example, who we think of as a rather serious character seems to have collected ‘freaks’. He had what writers at the time described as a live centaur - half-man, half-horse - sent to Rome from Arabia. Beard explains: “Whatever it really was, the poor creature died.”

Hadrian had a lover, Antinous, a lad aged about 18. The pair went on holiday to Egypt and Antinous accidentally drowned in the Nile. Hadrian went somewhat crazy with grief. He made Antinous a god and commissioned so many statues of his boyfriend that more images of Antinous exist today than almost any other figure from antiquity.

Evidently, emperors were subjected to endless flattery. One chap called Lucius was such a craven suck-up that he carried around the shoe of the emperor Claudius’s wife Messalina and would take it out and kiss it in public.

Perhaps, that’s why so many emperors trusted their slaves more than citizens. One slave, Musicus Scurranus became the effective chancellor of the exchequer. When he died, he had 16 of his own slaves, known as under-slaves.

Imperial women were also a means to tarnish an emperor’s place in history. Commodus was the delinquent son of Marcus Aurelius, seen as Rome’s ‘best emperor’ and a prototype ‘philosopher-king’, and his wife Faustina. After Commodus was assassinated it was much easier to degrade his mother than his much-loved father as a means of damning him in history.

So the story went that Commodus was actually the product of one of Faustina’s many affairs with rough-trade gladiators. That was also a fit with Commodus’s behaviour: he’d offended Roman elites by fighting as a gladiator in the arena. Gladiators were seen as on the same footing with sex workers in Rome.

Like our rulers today, all emperors were playing a part - just like Commodus posing as a gladiator. So, one final unifying characteristic is that emperors were basically ‘actors’, one way or another. How fitting that the first emperor Augustus recognised that truth on his death bed. As he lay dying, he asked some friends if he had “played his part in the comedy of life properly”, and added that “since the play has gone down well, give us a clap and send us away with applause”.

Little wonder Beard sees direct parallels between Nero scandalising Rome by taking to the stage as an actor (performers were another caste in the same bracket as sex workers), and Boris Johnson sculpting his ‘man-of-the-people’ image on TV shows like Have I Got News For You.

Plus ça change and all that, eh?

Mary Beard’s Emperor of Rome is out now in hardback from Profile Books priced £30