Roman conquest of Britain

The Roman conquest of Britain was the Roman Empire's conquest of 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.

In common with other regions on the edge of the empire, Britain 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 the 40s 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).

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.