The earliest evidence of human occupation around 900,000 years ago is at Happisburgh on the Norfolk coast, with stone tools and footprints probably made by Homo antecessor. The oldest human fossils, around 500,000 years old, are of Homo heidelbergensis at Boxgrove in Sussex. Until this time Britain was permanently connected to the Continent by a chalk ridge between south-east England and north-east France called the Weald-Artois Anticline, but during the Anglian Glaciation around 425,000 years ago a megaflood broke through the ridge, creating the English Channel, and after that Britain became an island when sea levels rose during interglacials. Fossils of very early Neanderthals dating to around 400,000 years ago have been found at Swanscombe in Kent, and of classic Neanderthals about 225,000 years old at Pontnewydd in North Wales. Britain was unoccupied by humans between 180,000 and 60,000 years ago, when Neanderthals returned. By 40,000 years ago they had become extinct and modern humans had reached Britain. But even their occupations were brief and intermittent due to a climate which swung between low temperatures with a tundra habitat and severe ice ages which made Britain uninhabitable for long periods. The last of these, the Younger Dryas, ended around 11,700 years ago, and since then Britain has been continuously occupied.
Britain and Ireland were then joined to the Continent, but rising sea levels cut the land bridge between Britain and Ireland by around 11,000 years ago. A large plain between Britain and Continental Europe, known as Doggerland, persisted much longer, probably until around 5600 BC. By around 4000 BC, the island was populated by people with a Neolithic culture. However, no written language of the pre-Roman inhabitants of Britain has survived; therefore, the history, culture and way of life of pre-Roman Britain are known mainly through archaeological finds. Although the main evidence for the period is archaeological, available genetic evidence is increasing, and views of British prehistory are evolving accordingly. Toponyms and the like constitute a small amount of linguistic evidence, from river and hill names, which is covered in the article about pre-Celtic Britain and the Celtic invasion.
The first significant written record of Britain and its inhabitants was made by the Greek navigator Pytheas, who explored the coastal region of Britain around 325 BC. However, there may be some additional information on Britain in the "Ora Maritima", a text which is now lost but which is incorporated in the writing of the later author Avienus. Archaeological evidence demonstrates that ancient Britons were involved in extensive maritime trade and cultural links with the rest of Europe from the Neolithic onwards, especially by exporting tin that was in abundant supply. Julius Caesar also wrote of Britain in about 50 BC after his two military expeditions to the island in 55 and 54 BC. The 54 invasion was probably an attempt to conquer at least the southeast of Britain but failed.
Located at the fringes of Europe, Britain received European technological and cultural achievements much later than Southern Europe and the Mediterranean region did during prehistory. The story of ancient Britain is traditionally seen as one of successive waves of invasion from the continent, with each bringing different cultures and technologies. More recent archaeological theories have questioned this migrationist interpretation and argue for a more complex relationship between Britain and the Continent. Many of the changes in British society demonstrated in the archaeological record are now suggested to be the effects of the native inhabitants adopting foreign customs rather than being subsumed by an invading population.
Palaeolithic (Old Stone Age) Britain is the period of the earliest known occupation of Britain by humans. This huge period saw many changes in the environment, encompassing several glacial and interglacial episodes greatly affecting human settlement in the region. Providing dating for this distant period is difficult and contentious. The inhabitants of the region at this time were bands of hunter-gatherers who roamed Northern Europe following herds of animals, or who supported themselves by fishing.
There is evidence from bones and flint tools found in coastal deposits near Happisburgh in Norfolk and Pakefield in Suffolk that a species of Homo was present in what is now Britain at least 814,000 years ago. At this time, Southern and Eastern Britain were linked to continental Europe by a wide land bridge (Doggerland) allowing humans to move freely. The species itself lived before the ancestors of Neanderthals split from the ancestors of Homo sapiens 600,000 years ago. The current position of the English Channel was a large river flowing westwards and fed by tributaries that later became the Thames and Seine. Reconstructing this ancient environment has provided clues to the route first visitors took to arrive at what was then a peninsula of the Eurasian continent. Archaeologists have found a string of early sites located close to the route of a now lost watercourse named the Bytham River which indicate that it was exploited as the earliest route west into Britain.
Sites such as Boxgrove in Sussex illustrate the later arrival in the archaeological record of an archaic Homo species called Homo heidelbergensis around 500,000 years ago. These early peoples made Acheulean flint tools (hand axes) and hunted the large native mammals of the period. One hypothesis is that they drove elephants, rhinoceroses and hippopotamuses over the tops of cliffs or into bogs to more easily kill them.