The known history of the horse in Britain starts with horse remains found in Pakefield, Suffolk, dating from 700,000 BC, and in Boxgrove, West Sussex, dating from 500,000 BC. Early humans were active hunters of horses, and finds from the Ice Age have been recovered from many sites. At that time, land which now forms the British Isles was part of a peninsula attached to continental Europe by a low-lying area now known as "Doggerland", and land animals could migrate freely between what is now island Britain and continental Europe. The domestication of horses, and their use to pull vehicles, had begun in Britain by 2500 BC; by the time of the Roman conquest of Britain, British tribes could assemble armies which included thousands of chariots.