According to Francis Bacon, the House of York was ‘a race often dipped in its own blood’. That being so, one wonders what Bacon made of Rome’s Julio-Claudian dynasty, the gore-spattered family that gave the empire its first five rulers, and the subject of Tom Holland’s latest popular history of the ancient world.

Recounting one of the era’s many fratricidal civil wars, Holland rightly observes: ‘The aptitude of the Roman people for killing, which had first won them their universal dominion, was now unleashed upon themselves.’ And no one was more adept at such incestuous slaughter than the imperial family itself.

The dynasty’s strongman founding father, Augustus, was probably the least murderous of the lot and had many positive reforms to his credit. After avenging his great-uncle Julius Caesar’s murder by destroying his assassins, and his own erstwhile ally Marc Antony, Augustus seized the reins of power himself. His achievements as ‘Princeps Civitas’ (‘first citizen’ rather than formal emperor) included expanding the empire by conquest, reforming its chaotic taxation system, creating the elite Praetorian Guard and restructuring the constitution to ease Rome’s path from a republic to a hereditary monarchy ruled by his own family.

When Augustus (unusually) died aged 75 in his own bed, apparently of natural causes, his widow Livia seized effective power, making her son by her first marriage, Tiberius, the new emperor. For it was a feature of the first family that its female members were at least as ruthless, rapacious and ambitious as their menfolk. Though he had been a successful soldier, Tiberius proved a dud emperor. Gloomy and fearful, he steered well clear of Rome, only occasionally launching Stalin-style purges of his relatives and rivals, and shut himself away on the island of Capri, where he devoted himself to sexual debauchery.

An ingenious pervert, Tiberius allegedly trained boys and even weaning infants in the art of swimming between his legs in his pool and performing fellatio upon him. Reporting such lurid stories, Holland is judicious in their presentation. Though his principal sources, the historians Suetonius and Tacitus, give him more than enough sensational material to paint a perverse picture of crime and decadence, he is careful in how he uses it and often acquits his subjects of the grosser accusations against them.

The next emperor, Caligula (the nickname, bestowed by his soldiers when he was a toddler, means ‘Bootee’), pampered favourite of his great-uncle Tiberius, could be accused of many things, but judicious moderation was not one of them. Schooled on Capri in the old emperor’s most arcane perversions, and apparently clinically insane as well as horribly vicious, the new ruler descended rapidly from an attractive and promisingly popular new broom, through the eccentricity of screwing his sisters, commanding his legions to harvest shells on a beach instead of invading Britain and making his horse a magistrate, to a mad tyrant who wished that the Romans had only one neck for him to sever.

After a mercifully short four-year reign, the Praetorian Guard did Rome a favour by assassinating Caligula and proclaiming his stuttering, foot-dragging uncle Claudius emperor. Overlooked by everyone, even his own family, Claudius reluctantly limped onto history’s stage and gave a surprisingly impressive performance. He proved an able administrator, and the province of Britain was added to the imperial dominions on his watch. But, as Holland makes very clear, Robert Graves’s portrayal of a humane and liberal ruler in Claudius the God is false: Claudius had hundreds executed, and delighted in promoting the bloodiest games to keeps the plebs happy.

His end, too, was typical of his psychopathic clan. His fourth wife, Agrippina, had him poisoned, probably with a dish of mushrooms, to make way for her own son, and Claudius’s great-nephew, the notorious Nero. (Naturally, Nero repaid mum by having her killed too.) Holland has no truck with modern revisionists who claim that the most disreputable of emperors has been misrepresented. His Nero fits the traditional picture of a whingeing, self-pitying nonce with a bizarre taste in garden illuminations: Christians dipped in pitch and set alight.

But beneath the obscene cavortings of their rulers, Holland never lets us forget that decent Romans thrived and Rome — despite Nero’s insurance-scam-style great fire — was built in all its gory glory. Even mad Caligula contributed to the city by constructing aqueducts. When Nero took his worthless life by slitting his own throat, Rome’s greatest days were still to come.