A few finds of Paleolithic tools indicate the use of the area by Old Stone Age hunters during previous inter-glacial periods, but the Forest as we know it originated in the Atlantic period: the warm, wet phase which followed the retreat of the last Ice Age in Britain, some 7000 years ago. Occasional Mesolithic flints show early hunter-gatherers utilised the Forest, and although there are a few Iron Age tumuli (burial mounds), the area seems to have been sparsely populated prior to the Roman period, on account of its unsuitability for farming.