When the ice finally withdrew from Scotland at the end of the last Ice Age the human history of Scotland began with the arrival of nomadic hunter-gatherer groups from around 12000 BC onwards which set the pattern for periodic influxes of differing peoples over the subsequent millennia. These new arrivals in the wake of the ice withdrawing were few in number at first and it is difficult to understand the environment they were travelling through, as there would be no other humans present there. They would quickly have had to develop new techniques and improvements to survive. This set the pattern for the future with new peoples bringing in new ideas, technology and foodstuffs. Life was hard and precarious for these first groups but gradually a more settled society developed based on agriculture which developed through the Neolithic, Bronze and Iron Ages down to the time of the Roman invasions. Though still precarious life at least became a little easier for people in these tribal based societies in spite of them still being on usually quite a small scale and far from comfortable by modern standards. The final arrivals before the Romans was of the Celtic peoples which produced profound changes to the existing settled agricultural society which are still disputed by historians to this day. However no-one doubts they brought profound changes to the existing society including to some extent making it more violent and hierarchical in nature.