Hadrian's Wall

By the year 122 AD, Rome ruled a vast empire, and it had grown tired of growing. For decades its legions had pushed north through Britain, but the far north — the cold, mountainous country of the tribes the Romans called Caledonians — was never truly conquered. The wars there were expensive, the raids across the border were constant, and the emperor Hadrian had seen enough. He was a soldier and a builder, and he preferred a fixed, defensible frontier to endless bloody conquest. When he visited Britain that year, his order was blunt: build a wall to separate the Romans from the barbarians.

What his army built was staggering. A stone wall ran roughly 73 miles across the whole neck of northern Britain, from the River Tyne in the east to the Solway Firth in the west — sea to sea. It was up to three metres thick and perhaps four or five metres high. A deep ditch was dug along the northern side; a military road ran along the south. Along its length stood a small fort at every Roman mile — a "milecastle" — with two watchtowers between each one, and larger forts holding hundreds of troops spaced out behind. It was the most heavily fortified line in the entire Roman world.

And yet it was never simply a barrier to hide behind. Gateways through the milecastles let approved people pass, north and south, under guard. The wall was a statement of power carved across the land — this far, and no further — but it worked, day to day, as an enormous checkpoint: a way to watch movement, tax the trade, and decide who crossed.

Here is the surprise at the heart of the story: the wall was built mainly by Roman legionaries, but it was not manned by Romans at all. The day-to-day garrison — some fifteen thousand soldiers strung out along the line — were auxiliaries, troops recruited from the many conquered peoples of the empire. On this one cold frontier you would find archers from Syria, cavalry from what is now Spain and Belgium, and infantry raised on the banks of the Rhine and the Danube. An empire built its northern edge with soldiers who had themselves been swallowed by it, and rewarded them, after twenty-five hard years, with Roman citizenship.

Life on the frontier was not the grim, empty siege we might imagine. Behind the wall, at forts such as Vindolanda, whole communities grew up: workshops, bath-houses, temples, and outside the walls a civilian town of families, traders and taverns. Thin wooden writing-tablets found preserved in the mud there have handed us the actual voices of these people. One is a letter about a parcel sent from home — socks, sandals and underpants, against the British cold. Another, written around the year 100, is an invitation from one officer's wife to another to come to her birthday party — the earliest surviving handwriting by a woman anywhere in the Roman world.

Between the boredom and the cold there was real danger too. The tribes beyond the wall did not go away, and patrols moved out through the gateways into hostile country. Every few years the northern peoples would raid across the line, and now and then the frontier erupted into open war. For the soldier from a warm province, posted for a quarter of a century to this grey, rain-soaked edge of the world, the wall could feel less like a posting than an exile.

The wall stood as a working frontier for the best part of three hundred years. It was manned, repaired, briefly abandoned for a wall built further north, and then reoccupied. But an empire cannot hold a line forever. By the early fifth century, Rome — pressed on every side and shrinking back towards Italy — pulled its army out of Britain for good. The garrisons drifted away, the pay stopped coming, and the great line across the north was simply left.

What followed was slower than any invasion. For fourteen centuries the wall became a quarry. Farmers, churches, villages and even a later road took its shaped stone away, until in many places the mightiest barrier in the Roman world had sunk to a low green ridge running across the moors. Yet it never vanished. It ran, and still runs, straight through the middle of Britain's imagination — a physical memory of the empire that once ruled here.

Today Hadrian's Wall is a World Heritage Site, and people walk its whole length coast to coast, tracing a line laid down nearly nineteen centuries ago. Beyond the surviving ruins, the deeper thing it left behind is a question the modern world has never stopped asking: where does a country draw its edge, who gets to cross it, and what does it cost to guard a line?