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 by AD 87, when the Stanegate was established. The conquered territory became the Roman province of Britannia. Attempts to conquer northern Britain (Caledonia) in the following centuries were not successful.

Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe, consisting of the countries England, Scotland and Wales. With an area of 209,331 km2 (80,823 sq mi), it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It is dominated by a maritime climate with narrow temperature differences between seasons. The island of Ireland, with an area 40 per cent that of Great Britain, is to the west—these islands, along with over 1,000 smaller surrounding islands and named substantial rocks, form the British Isles archipelago.