He has not yet made a horse his running mate, but Donald Trump can be compared to one of the most notorious of all Roman emperors, Caligula, according to best-selling historian Tom Holland.

Holland told the Hay festival there were fascinating parallels between the actions and success of Trump and what was going on in Rome 2,000 years ago.

Caligula has gone down in history as one of the maddest and baddest of all Roman emperors, a name synonymous with the worst excesses of absolute power.

But there was more to the story of Caligula, Holland said. He is not quite the psychopath of popular imagination and we can see similarities between what is happening now and then.

What is known for sure about Caligula, Holland said, is that he had a great love of spectacle and dressing up; and he enjoyed hurting and humiliating people.

The young Caligula spent six years on the island of Capri, where he often directed and appeared in spectacular pornographic tableaux for his great uncle, the emperor Tiberius – a man it was said, who enjoyed having swimming boys nibble at his private parts.

When Tiberius died Caligua left for Rome where his excessive tastes “were translated on to the most public stage of all – the imperial capital.”

He did things differently to his forebears, the polar opposite of Tiberius’s and, before him, Augustus’ moral strategy. “Caligula had no interest in, no stake in the traditional values of Rome. He despised them. And he despised them because he saw them as entrenching the prestige and status of the aristocracy.”

Caligula wanted to rule as an autocrat and he was contemptuous of the pretence that the senate had any power at all.

“What he did was to trample the dignity of the senatorial elite into the dirt and what he discovered in doing that was that the mass of the Roman people really enjoyed it.”

Holland said there were parallels with what Trump has done to the Republican establishment.

“Trump has said and done things that are utterly shocking by the standards of traditional political morality, but far from making him unpopular with the masses there is a sense in which he has become the toast of the people.”

As well as trampling down the elite, Caligula was – like Trump – a conscious populist and sponsored chariot races and made a huge six-horse chariot for himself, which he would drive around Rome showing off.

“He did all the things that the people thought an emperor should do … they loved him for it.”

Treating the senate like dirt meant he was able to crush any conspiracy with ease.

Caligula’s reputation has not been done any favours by his portrayal on TV and film. Different generations may remember John Hurt’s portrayal of him in the 1970s BBC TV series I Claudius and the shocking, invented, scene where he appeared with a bloody face after eating the foetus torn from his sister’s stomach.

Or Malcolm McDowell’s performance in the semi-pornographic 1979 film Caligula, produced by Penthouse supremo Bob Guccione.

The most famous story about Caligula, that he planned to make his horse his consul, is too often misinterpreted, said Holland.

It should not be seen as Caligula being unhinged – he was saying even the consulship, the highest office in Rome, was in his power. “It is a bitter, cruel joke about the reality of autocracy,” said Holland.

The knives were always out for Caligula but his downfall was entirely his fault, said Holland. “He just could not help himself.”

Caligula told a captain in the Praetorian guard that he sounded like a girl. And the Praetorian killed him.