Metal tools first appeared in Wales about 2500 BC, initially copper followed by bronze. The climate during the Early Bronze Age (c. 2500–1400 BC) is thought to have been warmer than at present, as there are many remains from this period in what are now bleak uplands. The Late Bronze Age (c. 1400–750 BC) saw the development of more advanced bronze implements. Much of the copper for the production of bronze probably came from the copper mine on the Great Orme, where prehistoric mining on a very large scale dates largely from the middle Bronze Age. Radiocarbon dating has shown the earliest hillforts in what would become Wales, to have been constructed during this period. Historian John Davies, theorises that a worsening climate after around 1250 BC (lower temperatures and heavier rainfall) required more productive land to be defended.