Several species of humans have intermittently occupied Great Britain for almost a million years. 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 had been permanently connected to the Continent by a chalk ridge between South East England and northern France called the Weald-Artois Anticline, but during the Anglian Glaciation around 425,000 years ago a megaflood broke through the ridge, and Britain became an island when sea levels rose during the following Hoxnian interglacial.