The Roman Empire conquered most of the island of Britain, which was inhabited by the Celtic Britons. It began in earnest in AD 43 under Emperor Claudius, and was largely completed in the southern half of Britain (most of what is now called England and Wales) by AD 87, when the Stanegate was established. The conquered territory became the Roman province of Britannia.
Following Julius Caesar's invasions of Britain in 54 BC, some southern British chiefdoms had become allies of the Romans. The exile of their ally Verica gave the Romans a pretext for invasion. The Roman army was recruited in Italia, Hispania, and Gaul and used the newly-formed fleet Classis Britannica. Under their general Aulus Plautius, the Romans pushed inland from the southeast, defeating the Britons in the Battle of the Medway. By AD 47, the Romans held the lands southeast of the Fosse Way. British resistance was led by the chieftain Caratacus until his defeat in AD 50. The isle of Mona, a stronghold of the druids, was attacked in AD 60. This was interrupted by an uprising led by Boudica, in which the Britons destroyed Camulodunum, Verulamium and Londinium. The Romans put down the rebellion by AD 61.
The conquest of Wales lasted until c. AD 77. Roman general Gnaeus Julius Agricola conquered much of northern Britain during the following seven years. In AD 84, Agricola defeated a Caledonian army, led by Calgacus, at the Battle of Mons Graupius. However, the Romans soon withdrew from northern Britain. After Hadrian's Wall was established as the northern border, tribes in the region repeatedly rebelled against Roman rule and forts continued to be maintained across northern Britain to protect against these attacks.
Background
In common with other regions on the edge of the empire, British tribes had enjoyed diplomatic and trading links with the Romans in the century since Julius Caesar's expeditions in 55 and 54 BC, and Roman economic and cultural influence was a significant part of the British late pre-Roman Iron Age, especially in the south.
Between 55 BC and the 40s AD, the status quo of tribute, hostages, and client states without direct military occupation, begun by Caesar's invasions of Britain, largely remained intact. Augustus prepared invasions in 34 BC, 27 BC and 25 BC. The first and third were called off due to revolts elsewhere in the empire, the second because the Britons seemed ready to come to terms. According to Augustus's Res Gestae, two British kings, Dubnovellaunus and Tincomarus, fled to Rome as supplicants during his reign, and Strabo's Geographica, written during this period, says Britain paid more in customs and duties than could be raised by taxation if the island were conquered.
By 40 AD, the political situation within Britain was in ferment. The Catuvellauni had displaced the Trinovantes as the most powerful kingdom in south-eastern Britain, taking over the former Trinovantian capital of Camulodunum (Colchester). The Atrebates tribe whose capital was at Calleva Atrebatum (Silchester) had friendly trade and diplomatic links with Rome and Verica was recognised by Rome as their king, but Caratacus' Catuvellauni conquered the entire kingdom some time after AD 40 and Verica was expelled from Britain.
Caligula may have planned a campaign against the Britons in AD 40, but its execution was unclear: according to Suetonius' The Twelve Caesars, he drew up his troops in battle formation facing the English Channel and, once his forces had become quite confused, ordered them to gather seashells, referring to them as "plunder from the ocean due to the Capitol and the Palace". Alternatively, he may have told them to gather "huts", since the word musculi was also soldier's slang for engineers' huts and Caligula himself was very familiar with the Empire's soldiers. In any case this readied the troops and facilities that would make Claudius' invasion possible three years later. For example, Caligula built a lighthouse at Bononia (modern Boulogne-sur-Mer), the Tour d'Ordre, that provided a model for the one built soon after at Dubris (Dover).
Preparations for the invasion under Claudius
In 43, possibly by reassembling Caligula's troops from 40, Claudius mounted an invasion force under overall charge of Aulus Plautius, a distinguished senator. A pretext of the invasion was to reinstate Verica, the exiled king of the Atrebates.
It is unclear how many legions were sent: only the Legio II Augusta, commanded by future emperor Vespasian, was directly attested to have taken part.
The IX Hispana, the XIV Gemina (later styled Martia Victrix) and the XX (later styled Valeria Victrix) are known to have served during the Boudican revolt of 60–61, and were probably there since the initial invasion, but the Roman army was flexible, with cohorts and auxiliary units being moved around whenever necessary.
Three other men of appropriate rank to command legions are known from the sources to have been involved in the invasion. Cassius Dio mentions Gnaeus Hosidius Geta, who probably led the IX Hispana, and Vespasian's brother Titus Flavius Sabinus the Younger. He wrote that Sabinus was Vespasian's lieutenant, but as Sabinus was the older brother and preceded Vespasian into public life, he could hardly have been a military tribune. Eutropius mentions Gnaeus Sentius Saturninus, although as a former consul he may have been too senior, and perhaps accompanied Claudius later.
Crossing and landing
The main invasion force under Aulus Plautius crossed in three divisions. The port of departure is usually taken to have been Bononia (Boulogne), and the main landing at Rutupiae (Richborough, on the east coast of Kent). Neither of these locations is certain. Dio does not mention the port of departure, and although Suetonius says that the secondary force under Claudius sailed from Boulogne, it does not necessarily follow that the entire invasion force did. Richborough had a large natural harbour, which would have been suitable, and archaeology shows Roman military occupation at about the right time. However, Dio says the Romans sailed east to west, and a journey from Boulogne to Richborough is south to north. Some historians suggest a sailing from Boulogne to the Solent, landing in the vicinity of Noviomagus (Chichester) or Southampton, in territory formerly ruled by Verica.
River battles
British resistance was led by Togodumnus and Caratacus, sons of the late king of the Catuvellauni, Cunobeline. A substantial British force met the Romans at a river crossing thought to be near Rochester on the River Medway. The Battle of the Medway raged for two days. Gnaeus Hosidius Geta was almost captured, but recovered and turned the battle so decisively that he was awarded the Roman triumph. At least one division of auxiliary Batavian troops swam across the river as a separate force.
The British were pushed back to the Thames. They were pursued by the Romans across the river, causing some Roman losses in the marshes of Essex. Whether the Romans made use of an existing bridge for this purpose or built a temporary one is uncertain.
Togodumnus died shortly after the battle on the Thames. Plautius halted and sent word for Claudius to join him for the final push. Cassius Dio presents this as Plautius needing the emperor's assistance to defeat the resurgent British, who were determined to avenge Togodumnus. However, Claudius was no military man. The Praetorian cohorts accompanied Emperor Claudius to Britain in AD 43. The Arch of Claudius in Rome says he received the surrender of eleven British kings with no losses, and Suetonius' The Twelve Caesars says that Claudius received the surrender of the Britons without battle or bloodshed. It is likely that the Catuvellauni were already as good as beaten, allowing the emperor to appear as conqueror on the final march on Camulodunum. Cassius Dio relates that he brought war elephants and heavy armaments which would have overawed any remaining native resistance, though the claim Claudius brought elephants to Britain has been doubted by modern historians, and may refer to a military machine, perhaps a siege tower, instead. Eleven tribes of South East Britain surrendered to Claudius and the Romans prepared to move further west and north. The Romans established their new capital at Camulodunum and Claudius returned to Rome to celebrate his victory. Caratacus escaped with his family, retainers, and treasure, to continue his resistance further west.
After the invasion Verica may have been restored as king of the Atrebates; although by this time he would have been very elderly. In any case a new ruler for their region, Cogidubnus, soon appeared as his heir and as king of a number of territories following the first stage of the conquest as a reward as a Roman ally.
AD 44–60
Vespasian took a force westwards, subduing tribes and capturing oppida settlements as he went. The force proceeded at least as far as Exeter, which became a base for the Roman legion, Legio II Augusta, from 55 until 75. Legio IX Hispana was sent north towards Lincoln (Latin: Lindum Colonia) and by 47 it is likely that an area south of a line from the Humber to the Severn Estuary was under Roman control. That this line is followed by the Roman road of the Fosse Way has led many historians to debate the route's role as a convenient frontier during the early occupation. It is unlikely that the border between Roman and Iron Age Britain was fixed with modern precision during this period.
Late in 47 the new governor of Britain, Publius Ostorius Scapula, began a campaign against the tribes of modern-day Wales, and the Cheshire Gap. The Silures of southeast Wales caused considerable problems to Ostorius and fiercely defended their border country. Caratacus himself led this guerilla campaign but was defeated when he finally chose to offer a decisive battle; he fled to the Roman client tribe of the Brigantes who occupied the Pennines. Their queen Cartimandua was unable or unwilling to protect him however, given her own accommodation with the Romans, and handed him over to the invaders. Ostorius died and was replaced by Aulus Didius Gallus who brought what are now the Welsh borders under control but did not move further north or west, probably because Claudius was keen to avoid what he considered a difficult and drawn-out war for little material gain in the mountainous terrain of upland Britain. When Nero became emperor in 54, he seems to have decided to continue the invasion and appointed Quintus Veranius as governor, a man experienced in dealing with the troublesome hill tribes of Anatolia. Veranius and his successor Gaius Suetonius Paulinus mounted a successful campaign across North Wales, famously killing many druids when he invaded the island of Anglesey in 60. Final occupation of Wales was postponed however when the rebellion of Boudica forced the Romans to return to the south east in 60 or 61.
AD 60–78
Following the successful suppression of Boudica's uprising in 60 or 61, new Roman governors continued the conquest by edging north.
Conquests to the North
The casus belli presented itself in 69 when Cartimandua queen of the Brigantes following a rebellion by her husband Venutius was forced to ask the Romans for aid, who evacuated her leaving Venutius in power. About Venutius one speculation is that he might have been a Carvetian and may therefore have been responsible for the incorporation of Cumbria into a Brigantian federation whose territory straddled Britain along the Solway-Tyne line; furthermore Cartimandua may have ruled the Brigantian peoples east of the Pennines (possibly with a centre at Stanwick, Yorkshire), while Venutius was the chief of the Brigantes west of the Pennines (or Carvetii), in Cumbria (with a possible centre based at Clifton Dykes).
In any case Tacitus says that in 71 Cerialis (governor AD 71–74) waged a successful war against the Brigantes. He praises both Cerialis and his successor, Julius Frontinus (governor 75–78).
Much of the conquest of the north may have been achieved under the governorships of Vettius Bolanus (governor AD 69–71), and of Quintus Petillius Cerialis. From other sources it seems that Bolanus had possibly dealt with Venutius and penetrated into Scotland, and evidence from the carbon-dating of the gateway timbers of the Roman fort at Carlisle (Luguvalium) suggests that they were felled in AD 72, during the governorship of Cerialis. Lead ingots from Deva Victrix, the Roman fortress at Chester, indicate that construction there was probably under way by AD 74.