Mull and its islands have been continually inhabited since they became environments able to support man after the Ice Age. C. 6500 - 3500 BC. Mesolithic hunter-gatherers lived in caves such as Livingston's cave on Ulva. C. 4000 - 2000 BC Neolithic farmers people lived here leaving behind burial cairns and stone axes. C. 2500 - 600 BC. Bronze age 'Beaker' people lived on Mull, their burial cairns, cists, standing stones, stone circles, and corded beaker pottery and knife blades record their existence. C. 600 BC - c. AD 400 Iron Age peoples built forts, brochs, duns, and crannogs, - numerous defensive settlements on these islands. The early Christian period began in the 5th Century, with 563 noted for the arrival from Ireland of St Columba. Viking times started in 795 when Iona was first sacked, raids continuing for several centuries. Vikings eventually became settlers in the isles. The Middle Ages saw the construction of castles such as Moy and Duart, and chapels such as Pennygown. The clans were, Maclean, MacLaine, MacKinnon, Macquarrie, and MacDonald. During the 17th to 19th centuries, clan chiefs and other lairds built 'big' houses, whilst the majority of islanders lived in tiny black houses in small townships, occupying shielings in the summer months. In 1788 Tobermory was built by the British Fisheries Society, as a planned settlement. Over the centuries Mull's population increased to 10,638 in 1831 but first the Potato Famine and then the Clearances rapidly reduced this number. By the 20th Century much of the population had emigrated and there were more sheep on Mull than people.