To the Roman emperors of the first century A.D., Britain (or Britannia, as that remote territory was known) must have seemed beyond the pale of the civilized world, culturally inferior to the great cities of the empire.

The Romans nonetheless coveted these northern lands, if only as another jewel in the empire’s crown. The second-century A.D. historian Florus (a name used by three, more-or-less contemporaneous writers) observed that the annexation of Britain had no benefit other than to add luster “to the bearing of imperial power.”

The Romans first invaded Britain in 55 B.C., under Julius Caesar, who had conquered Gaul in a bloody campaign that began in 59 B.C. Caesar no doubt believed that another show of military might would impress the political elite in Rome. Caesar left Gaul with two legions of soldiers, most likely landing at Kent, on England’s southern coast. Although the Romans fought hard and were victorious in battle, hostile weather forced them to retreat to Gaul. Caesar returned the following year with five legions, triumphing again over the local tribes of Britain. The indigenous tribes could muster little defense, after all, against the javelins and short swords of the armored Roman infantries.

Gaul (and later, the German frontier), however, required much more attention than did Britain, and the Romans failed to capitalize on Caesar’s early successes. The political instability caused by civil war in the empire meant that a century would pass before Rome truly conquered Britain. In 43 A.D., under the orders of the emperor Claudius (41–54 A.D.), a commander named Aulus Plautius led some 20,000 men into Britain, winning a series of military victories. Claudius himself arrived in the fall of 43 (along with thousands of reinforcements and the first elephants to tread upon British soil) and decided to make Britain a Roman province—though the pacification and occupation of Britain would be painstakingly slow.

The success of imperial rule in Britain was often connected to the state of affairs back in Rome. When Rome was immersed in turmoil, when it suffered revolts and incursions from within, the Roman military commitment abroad consequently waned. On June 9, 68 A.D., for example, a politically embattled and disconsolate Emperor Nero supposedly uttered a final regret—”What an artist the world is losing”—before stabbing himself in the neck. The infighting that followed the emperor’s suicide destabilized the empire, and Rome’s control over Britain was weakened.

Beyond Roman Britain’s northern boundary were the Celtic tribes that frequently launched raids into Roman territory. (Celtic peoples had appeared in Germany around 800 B.C. and had eventually spread throughout Europe.) Several times the Romans tried to march northward and conquer what is now Scotland; one aspect of this northern campaign was the construction of a line of forts, including Vindolanda. In 105 A.D., however, the Romans were forced to return south. This sort of advance and retreat would become common practice for the duration of Roman-British history.

The northern frontier was far from settled when the emperor Hadrian (117–138 A.D.) visited Britain in the summer of 122 A.D. Hadrian was famous for visiting the many distant outposts of the empire to inspect the workings of local government and project Roman glory to the frontier. According to the Augustan History, a collection of imperial biographies written in the late fourth century A.D., the emperor, “having completely transformed the soldiers” of the Roman army, “set right many things” in Britain, and then “drew a wall along a length of eighty miles to separate barbarians and Romans.”

Hadrian’s stone wall, between 8 and 10 feet thick and with castellated defenses on either side, was completed in 139 A.D. Although the Roman frontier position was now strengthened, the northern tribes would continue to be nettlesome, and Hadrian’s Wall had to be refortified from time to time.

In the second century A.D., Londinium (present-day London)—the timber and mudbrick settlement that had been built soon after Claudius’s invasion—had become the provincial capital. By mid-century, the larger towns in Britain had become largely Romanized—in fashion, religion and culture. Waterways were improved, and roads were built that allowed for easier communication. The towns of Britain took on an increasingly Roman aspect, with street plans based on the rectilinear grid, and with forums and basilicas dominating urban life. (Before the Romans came, Britain had no organized urban centers, only towns that somewhat resembled the fortified settlements [oppida] of the Roman world.) Trade increased, agriculture became more developed, sanitation improved. In the southern British countryside, lavish Roman-style stone villas arose.

Even as its towns grew in size and stature, Britain’s frontier problem did not disappear. In 142 A.D. the Romans pushed north again into southern Scotland, this time under the orders of the emperor Antoninus Pius (138–161 A.D.)—though unlike Hadrian, Antoninus did not travel to Britain himself. The Romans advanced beyond Hadrian’s Wall and constructed a second rampart, built of turf, stone and wood, some 10 feet tall and 13 feet thick. The Antonine Wall, as the structure came to be known, stretched 37 miles. However, the forts built in conjunction with the new wall were abandoned within two decades; the newly claimed territories were simply too difficult to defend, and by 160 A.D. the northern edge of the frontier was again defined by Hadrian’s Wall.

The emperor Septimius Severus (193–211 A.D.) decided to solve the frontier issue for good, aiming to conquer Scotland and bring all of Britain under Rome’s imperial control. In 208 A.D., accompanied by his son Caracalla (the future emperor), the ambitious Severus, despite his advanced age and poor health, led the Roman army into Scotland. The years 209 and 210 saw a good bit of military success, but on February 4, 211, Severus died. Caracalla, who did not share his father’s vision of a unified, conquered Britain, returned to Rome, leaving the Scottish conquest unfinished.

Even though its southern part flourished for many years, Roman Britain repeatedly proved vulnerable to outside attacks. The Franks and the Saxons—warlike Germanic tribes—carried out raids with particular success. Fed up with Rome’s inability to defend Britain, a general named Postumus decided to form his own renegade empire in 260, wresting control of Britain and Gaul from Rome. Though Postumus was killed (by his own soldiers) in 268, the Gallic empire he created survived until 274, when its third emperor, Tetricus, ceded lands back to the Roman emperor Aurelian.

Foreign agitation would not cease, however. In 367 an invasion of combined forces—including the Picti from the north, the Irish, the Saxons, the Scoti from Ireland and the supposedly cannibalistic Attacotti—wrought widespread devastation. By 400 three “barbarian” kingdoms were occupying the terrain north of Hadrian’s Wall: Strathclyde, Gododdin and Galloway.

The decline of Roman Britain was punctuated by an act of abandonment, as it were. Because Roman soldiers were constantly being recalled to defend other parts of the empire, Britain remained vulnerable, particularly to the Picti and the Saxons. In 410 Roman-Britons who were disillusioned with the attacks petitioned the emperor Honorius (395–423) for help. But Honorius had other problems to deal with, namely the Visigothic leader Alaric, who captured Rome that very year. Honorius wrote that he was powerless to help the Roman-Britons and that they must “look to their own defenses.”

Honorius’s letter clinched Britain’s fate. Some Romans did stick around in Britain until approximately 450, but some four centuries of Roman rule had officially come to an end.