The Ice Ages began in Britain just over two and a half million years ago. They were characterised by periods of extremely cold weather, when glaciers formed and when most of the land that was later to form the British Isles was uninhabitable. The earliest humans arrived in Britain around a million years ago, but would only have been able to live here, sometimes in sheltering caves, in the warmer spells, known as interglacials, between the glaciers. The last interglacial ended about 72,000 years ago and the humans who lived here were close relatives known as Neanderthals. Modern humans (Homo sapiens) arrived in Britain as the climate began slowly to warm up towards the end of the last glacial period, from about 40,000 years ago.