When humans first came to Britain, at least 500,000 years ago, it was still connected by land to mainland Europe. A chalk ridge linked the area of modern Kent to northern France which meant people could travel to Britain by land. Sometimes the land connection was much bigger. During times when the climate was warm, the sea-level was similar to the present day, but as the climate cooled, sea-levels dropped due to water becoming frozen as ice on the Poles. At times sea-level dropped by as much as 100m, turning the North Sea into a flat plain that linked eastern England to Belgium and the Netherlands.

At some point at the end of an ice-age (perhaps 450,000 or possibly 250,000 years ago), water in the North Sea forced a passage through the ridge of chalk that linked southern England to northern France. This created the Straits of Dover meaning that during warm phases Britain was an island. It was only during cold phases when sea-level dropped, that Britain once again became joined to mainland Europe.

These changes in the geography of Britain had an important effect on when humans could get to Britain by land. After the creation of the Straits of Dover, access would have been limited to cool or cold periods.