Who will guard the guards?

The history of an army is essentially the history of its deeds. The history of an army within an army is more intriguing. The Praetorian Guard, a modern term, was founded, or rather formalised, around 27 BC by Augustus for the protection of the emperor and his family. Hitherto, cohors praetoria had been a generic description of the body of troops detailed, ad hoc, for the protection of a general on campaign. This derived from praetorium, the general’s tent next to which they were quartered in camp, which itself derived from praetor, ‘the man who goes before others’. As Gaius Octavius (Octavian) metamorphosed into the first emperor, Augustus, so his cohors praetoria multiplied to become the Praetorian Guard — cohortes praetoriae, the name by which the Romans knew them.

With ten cohorts, each of about 1,000, towards the end of Augustus’s reign — rising perhaps to 15,000 during that of his successor Tiberius — the guard, although relatively small compared with the army as a whole, gradually became the power behind the throne, almost literally so after the building of the Castra Praetoria (to house the cohortes, therefore plural) on the edge of Rome. With accommodation for 15 cohorts, it was ‘a reminder that the emperor’s power was ultimately determined by his capacity to command and control the military force that made the regime possible’.

Indeed, the Castra’s builder, the praetorian prefect Lucius Aelius Sejanus, played with memorably reptilian charm by Patrick Stewart in I Claudius (1976), would himself try to seize the imperial crown, and having failed would pay the price, of course, at the hands of his own praetorians.

These formidable servants of the emperor ‘could either make or break him’, writes Guy de la Bédoyère in this absorbing account of just how they did so variously in the three-and-a-half centuries until Constantine disbanded them in AD 312 and demolished the greater part of their barracks.