But this was not the only shadow darkening the millennial celebrations. Trouble was brewing beyond the frontiers of the empire as well as within them. In Virgil’s great poem, the Roman people had been promised a “dominion without limit”;9 but the truth was, as their strategists were perfectly well aware, that there were limits to everything. Just as there lay beyond the bulwarks of Iranshahr a terrifying immensity of nomad-infested grasslands, so likewise, beyond the northern reaches of Rome’s empire, there stretched a whole wilderness of bogs and forests: one that seemed positively to seethe with barbarians. The conundrum of how best to ward off these savages was one that had been perplexing the Roman high command for centuries. Too backward to be worth the effort of conquering, they were simultaneously too menacing simply to be left to run amok. A knotty problem—and one that had required an appropriately deft-fingered response. Roman frontier policy took many forms. Watchful defence on the part of the legions was punctuated by bursts of pulverising aggression. Submissive tribes could expect to be rewarded with grants of gold; defiant tribes with slaughter and ruin. On occasion, the Roman military also turned the barbarians’ seemingly inexhaustible relish for fighting to its own advantage by employing whole groupings of them—foederati—alongside the legions. Rome’s aim, of course, was quite simple: to maintain a crushing superiority. In this, for most of the long period of peace ushered in by Augustus, she had been resoundingly successful. Increasingly, though, along the entire northern frontier, there were alarming signs that the balance of power might be shifting. Raids across the Rhine had been going on for decades. Further east, across the Danube, a people called the Goths had recently launched even more brutal incursions. In the year of the millennium itself, they torched whole swaths of the Balkans. All this had come as a most unpleasant surprise to the Roman authorities. It seemed scarcely believable that warlords right on the doorstep of the empire were capable of planning, leading and executing such devastation. Barbarians were simply not meant to be capable of organising themselves on such a scale. Patently, however, what had once been scattered tribal groupings were now starting to cohere into something more. Their leaders, it seemed, freighted with Roman subsidies and plunder, had been deploying this treasure to broaden their own horizons. The richer in gold they were, the more weight they had to throw around. War bands that had once numbered hundreds might now very well number thousands. This, while hardly muscle on an imperial scale, did mean that barbarian kings were increasingly packing a heavy punch. They had become, in short, just that little bit more Roman.
Which did not, of course, make them any the less contemptible. In fact, if anything, the clod-hopping of the Goths deep into the heartlands of the empire only confirmed the Romans in their scorn. The true, the ultimate shock to their complacency did not come from the North, but from the East. Rome was not yet, as she celebrated her millennium, prepared to acknowledge Persia as an equal. Nevertheless, barely two decades after Ardashir had seized the throne, she had been given a foretaste of what was to come. Shapur I, Ardashir’s son, had already expelled the Romans from Mesopotamia for good. The imperial high command, in a desperate attempt to preserve the remainder of Rome’s provinces in the East, had been obliged to denude the Rhine and the Danube of troops. Then, in 244, with the emperor himself on campaign in the East, there was yet another coup. The new Caesar, a hard-bitten warrior named Philip, was frantic to return from the front to Rome to shore up his position. He duly sued for peace. The truce, when it was agreed, came at monstrous cost—and Shapur made sure that the whole world knew it. It was Philip who would be portrayed on the cliff face just west of Persepolis grovelling before the triumphant Shahanshah. It was Philip as well, four years later, in the April of 248, who enjoyed the supreme honour of presiding over Rome’s millennium celebrations.
A few months later, in 249, he was dead: killed in battle by a rival Caesar named Decius. Two years on, Decius himself was hacked to pieces by a Goth war band. A decade after that, the dignity of the imperial throne reached its nadir, when Shapur captured the latest emperor, Valerian, and used him from that moment on as his mounting block. For the Persians, a living, breathing Caesar was the ultimate in trophies; and they duly made sure to record Valerian’s humiliation alongside Philip’s on the cliff face just west of Persepolis. Even death did not bring an end to the humbling of the wretched emperor: his skin, flayed from his body after his death and dyed a lurid red, was lovingly preserved in a temple as one of the supreme treasures of the House of Sasan.10
For the Romans, however, even worse was to come. More than the dignity of the imperial title was in meltdown by now. Events were slipping terrifyingly out of control. The more unstable the situation became, the more rival warlords were tempted to snatch after the ultimate prize. The more that happened, the more the eastern provinces were left exposed. The more that the Roman high command then moved troops to stabilise the front with Persia, the more it left the northern frontier open to the barbarians there. The more that the Goths and assorted other savage people then broke through to the rich, soft lands of the south, the more unstable conditions became. How to break this vicious circle? The dominion of the Roman people, it appeared, was locked into a death spiral.