But a biography written more than 200 years after Hadrian's death links the emperor to the wall: "Hadrian was the first to build a wall, 80 miles long, to separate the Romans from the barbarians."
One thing that is clear is that the wall was built at the end of an extraordinary period of expansion. From its earliest days, the Roman army had a hard time staying put. Led by generals hungry for glory—and perhaps a shot at becoming emperor—the legions constantly sought new conquests. From the first century B.C., a string of ambitious leaders pushed the boundaries of the empire steadily outward, to Britain and elsewhere. Julius Caesar crossed the English Channel in 55 B.C. and returned a year later. In A.D. 43, Claudius invaded England near Richborough, in Kent, and his successors pushed the island's Roman frontier north. By the end of the first century, Roman troops had forced their way deep into what is now Scotland. Trajan, crowned emperor in A.D. 98, fought wars in Dacia (present-day Romania), Parthia (Iran) and Germania.
When Trajan died in 117, his protégé Hadrian—an experienced military commander born into a prominent family, who spoke Greek, wrote poetry and took an interest in philosophy and architecture—inherited an empire and an army stretched to the breaking point. "He realizes they've expanded too far, too fast," Birley said. "Somehow he has to get the message across: ‘This far, no farther.'"
In 122, Hadrian visited Britain, and though his exact itinerary isn't known, historians believe that he toured the frontier. What better way to define the edge of his empire and keep his army out of trouble, the emperor-architect might have decided, than a monumental stone wall?
After a night at Greencarts Farm, just west of Chollerford, the morning dawned gray and cold. As I sat on the porch taping my bruised feet and lacing my muddy boots, the landlady brought the bill. "Just remember, there's always the bus," she said. Her accent rounded "bus" into a gentle "boose." I headed out through the farmyard into a drizzle, weighing her words carefully.
My spirits picked up almost immediately. At the edge of the farm, the wall reappears, rising to five or six feet in some spots. I soon climbed out of the low, rolling farm country to the top of the Whin Sill, a jagged ridge jutting hundreds of feet above the valley. It's lined with unbroken stretches of wall for miles at a time. Over the next two days, the wall was an almost constant presence. This center section, roughly ten miles long, remains the most rural, unspoiled and spectacular part of the walk.
At mile 36, I came upon Housesteads, a five-acre fort known to the Romans as Vercovicium ("hilly place" or "the place of effective fighters"). Draped over the lush green hillside, its extensive ruins were excavated more than a century ago; even so, the site is daunting. This was no temporary outpost: the commander's house had a courtyard and a heated room, the fort's latrines had running water and there was a bathhouse for the troops.
West of the fort, the wall climbs to Highshield Crags. Following the wall as it runs steeply up and down took my breath away. One can hardly imagine the ordeal the builders endured dragging the stones, lime and water up these rugged peaks—a ton of material for each cubic yard of masonry. The wall, according to some estimates, contains more than 1.7 million cubic yards.
Atop the ridge at least 100 feet above the valley and barricaded behind their stone wall, Roman soldiers must have gazed north with a sense of mastery. An earthwork consisting of a ditch 10 feet deep and 20 feet across and with two mounds on either side, known as the Vallum, ran just south of the wall, where there was also a wide road to move troops from one post to the next. On long stretches of the wall's north side, another deep ditch posed yet another obstacle. In some places the ditches were carved out of solid bedrock.
What were the Romans so worried about? Breeze says the Roman frontier wasn't primarily about defending the empire against barbarian attacks, as some archaeologists have argued. "Built frontiers aren't necessarily about armies attacking, but about controlling the movement of people," he says. "The only way you can fully control things is to build a barrier." Used for administrative control, not warding off invasion, it funneled people through designated access points, such as the gates that appear at regular intervals along the wall. The wall, he suggests, was more of a fence, like the one that runs along parts of the United States-Mexico border.