One of the things I love about the Decline and Fall of the Roman Empire is the artful way analysis and commentary are slipped in just where they seem to belong. A good example is found at the start of Chapter Five where we are treated to an explanation of the role of the army and in particular of the Praetorian Guard in Roman politics.
Gibbon was a member of parliament and counted among his friends the leading statesman of his day. I imagine that it was during some smoky late night port drinking session that he picked up this interesting observation.
Political scientists had concluded that it was impossible for a state to keep more than one percent of its population under arms for any length of time. This would be a handy rule of thumb to keep in mind if you were a foreign minister negotiating a treaty or forming an alliance to further your ends in the devious melange of seventeenth century international relations.
But Gibbon, the enlightenment thinker and historian could see another use for this tit bit of information.
The figure could be applied to the Roman Empire. Europe was still pre-industrial and despite some technological progress basic food production was still done in much the same way as it had been in the time of the Romans. He goes on to point out that although the proportion of men under arms in any state might be the same, the size of the state makes a huge difference. One man on his own, no matter how strong or well armed, cannot overwhelm another hundred. In a small settlement, a hundred armed men could not hope to defeat ten thousand peasants. But an army of one hundred thousand would be, if well organised and well led, easily capable of holding down a population of ten million.
In the second century the Roman Empire had a population of about 50 million and about 440,000 troops, very close to the one percent estimate. These troops were intended mainly to enforce the power of the emperor over the citizens rather than to defend the empire against external threats. The Praetorian guard, the most elite soldiers, were stationed not in the most precarious section of the frontier but in the capital.
The Praetorian Guard dated back to the time of Augustus, although he had been discrete enough to keep most of them near Rome rather than in the city itself. Tiberius moved them into a camp high on one of the hills over the city near the imperial palace. This brought them directly into the politics of the empire and their leader, the Praetorian prefect began to assume more and more significance. But even so, their summary removal of Pertinax from the head of the government was unusual. The removal of his head from his body even more so. The guards were powerful and arrogant, but they usually did their business behind closed doors.
Normally, a veneer of respectability was maintained. On the accession of a new emperor, he was expected to provide a donative in the form of hard cash – a large one off payment to every soldier. The name makes it sound like a generous gift from a monarch to a faithful servant. Protection money would have been a more accurate description. Any emperor who didn't get the troops on his side on day one had much less chance of getting to day two and beyond. Decorum was usually maintained, but the example of Pertinax showed the reality of where power came from.
On the day of his death, rumour got out that something was up and the crowds came out onto the streets in some disorder. Sulpicianus the governor of the city was attempting to restore the situation when news came from the palace. The news took the form of a group of troops bearing the head of Pertinax on a pike. This would be a gruesome enough sight for anyone, but Sulpicianus was the father-in-law of Pertinax. Despite this, he rushed to the palace to start negotiating to take over the now vacant post.
This was not in the best possible taste given that his son-in-law's headless body was still warm. But it was pragmatic. As a prominent figure in the regime, and one with a claim to succession, he would be at considerable risk if someone else took over.
For the Praetorians, Sulpicianus was as good a choice as anyone. The sticking point though seems to have been the size of the donative. The Praetorians may have been disloyal but you couldn't accuse them of having a poor head for business. To make sure that they got the best possible price they decided to introduce some healthy competition to the process. They shouted from the battlements for anyone interested in the throne to come forward with an offer. The empire was openly up for public auction.
And a bidder duly appeared. It is after all a rare opportunity to be able to buy the world. An elderly senator called Didius Julianus had both the money and the inclination. Sulpicianus had offered a donative of 5,000 drachmas per man. But Julian outbid him with an offer of 6,500 drachmas.
He was declared emperor and marched through the city by troops in close combat formation. They swore their allegiance to him and then the Senate was assembled and was addressed by its new leader - surrounded by troops. Nobody dared oppose the selection.
He then entered the palace. In the excitement, nobody had thought to remove the headless body of Pertinax. The frugal supper intended for the former emperor was still on the table. Julian ordered a splendid feast and spent the evening enjoying a dancing show and playing dice.
But Gibbon supposed that he spent a sleepless night reflecting on the folly of assuming the throne with so little support. He now had to hold on to an empire that had 'not been acquired by merit, but that had been purchased by money.'