It is believed that at the end of the Neolithic Period (around 4000 BC), Achill had a population of 500-1,000 people. The island would have been mostly forest until the Neolithic people began crop cultivation. Settlement increased during the Iron Age, and the dispersal of small promontory forts around the coast indicate the warlike nature of the times. Megalithic tombs and forts can be seen at Slievemore, along the Atlantic Drive and on Achillbeg.