During the reign of the emperor Hadrian, the Roman Empire, which had arisen around 27 B.C. from the political rubble of the Roman Republic, changed its military and imperial strategy from expansion to defense. Having rapidly grown to an enormous area, the empire realized that it would have difficulties retaining its already-annexed territories, and that further expansion would bring the empire to an untenable and unsustainable size.
Hadrian was born in 76 A.D., became emperor in 117, and died in 138. He and his successors reconfigured to the Roman military hold the external borders of the empire against threats like the Germanic tribes, the Scots, and the Irish.
The Romans had expanded northeast into Germanic territory. The seemingly natural boundary between the Romans and the Germanic tribes was the line connecting the Rhine and Danube rivers. When the Roman placed settlements northeast of this line, they soon realized that they had overextended themselves, and needed to pull back. Hadrian ordered a sort of strategic retreat, surrendering the territory to the Germanic tribes. Historian Andrew Curry writes:
Hadrian may simply have recognized that Rome’s insatiable appetite was yielding diminishing returns. The most valuable provinces, like Gaul or Hadrian’s native Spain, were full of cities and farms. But some fights just weren’t worth it. “Possessing the best part of the earth and sea,” the Greek author Appian observed, the Romans have “aimed to preserve their empire by the exercise of prudence, rather than to extend their sway indefinitely over poverty-stricken and profitless tribes of barbarians.”
The Rhine was difficult to cross, and formed an obvious natural boundary. While there was some valuable farmland on the far side of it, the Roman drive to expand, in this case, was based more on pride than on the value of this particular piece of land to the empire.
Although wise, Hadrian’s policy was not an easy sell to the expansionist Roman collective ego. The glory of Rome had been its ability to continuously expand, and to do so quickly and easily. Hadrian had to convince the Romans, and especially the Roman military, that they should stop overreaching. Quote fellow historian Anthony Birley, Andrew Curry writes:
The army’s respect for Hadrian helped. The former soldier adopted a military-style beard, even in official portraits, a first for a Roman emperor. He spent more than half of his 21-year reign in the provinces and visiting troops on three continents. Huge stretches of territory were evacuated, and the army dug in along new, reduced frontiers. Wherever Hadrian went, walls sprang up. “He was giving a message to expansion-minded members of the empire that there were going to be no more wars of conquest,” Birley says.
Hadrian transformed the Roman army in significant ways. Instead of a mobile force for attacking and invading, it became a stationary defensive force.
The Roman army began to build substantial structures of wood and stone. It was attempting to established a clear, permanent, and defendable border.
By the time the restless emperor died in 138, a network of forts and roads originally intended to supply legions on the march had become a frontier stretching thousands of miles. “An encamped army, like a rampart, encloses the civilized world in a ring, from the settled areas of Aethiopia to the Phasis, and from the Euphrates in the interior to the great outermost island toward the west,” Greek orator Aelius Aristides noted proudly, not long after Hadrian’s death.
Probably the most famous of these border structures is Hadrian’s Wall, separating England from Scotland. On the island of Great Britain, the Romans had successfully occupied the southern half, but the Scots proved unconquerable.
The wall cut the island in half, from coast to coast: a spectacular engineering and construction feat.
That “outermost island” was where Hadrian built the monument that bears his name, a rampart of stone and turf that cut Britain in half. Today Hadrian’s Wall is one of the best preserved, well-documented sections of Rome’s frontier. Remnants of the 73-mile barrier run through salt marshes, across green sheep pastures, and for one bleak stretch not far from downtown Newcastle, alongside a four-lane highway. Miles of it are preserved aboveground, lining crags that rise high above the rain-swept countryside.
While spectacular, Hadrian’s Wall is not the only, and not the greatest, civil engineering accomplishment of the Roman army. In central Europe, a 31-mile section of the wall there is so close to perfectly straight that it deviates only 36 inches over its course.
The total mileage of the Limes wall between the Rhine and the Danube exceeds that of Hadrian’s Wall in Britain, and the physical structure of the wall and its accompanying watchtowers, barracks, and garrisons is more complex.
More than a century of study has given archaeologists an unparalleled understanding of Hadrian’s Wall. The wall, perhaps designed by Hadrian himself on a visit to Britain in 122, was the ultimate expression of his attempt to define the empire’s limits.
Although the wall on the northern border of England is called “Hadrian’s Wall,” the walls in central Europe and other remote parts of the empire are equally his.
