contact rather than mass invasion, and systems of kingdoms developed. Larger fortified settlements expanded, such as the Votadini stronghold of Traprain Law, East Lothian, which was the size of a town. Huge numbers of small duns, hill forts and ring forts were built on any suitable crag or hillock. The spectacular brochs were built, most impressively the nearly complete Mousa Broch, Shetland. Many Souterrain underground passageways were constructed, though their purpose is obscure. Island settlements linked with land by a causeway, the crannogs, became common; it is thought that their function was defensive. See also Timeline of prehistoric Scotland Prehistoric Orkney Prehistoric Britain List of prehistoric structures in Great Britain Early history of Ireland Genetic history of the British Isles References Further reading Scotland Since Prehistory: Natural Change and Human Impact, by Christopher Smout, 1993, Scottish Cultural Press, Mesolithic Scotland and Its Neighbours, by Alan Saville, 2004, Society of Antiquaries of Scotland, Scotland: From Prehistory to the Present, by Fiona Watson, 2003, The Early Prehistory of Scotland, by Tony Pollard and Alex Morrison, 1996, The Later Prehistory of the Western Isles of Scotland, by Ian Armit, 1992, Prehistoric Scotland, by Ann MacSween and Mick Sharp, 1989, Guide to Prehistoric Scotland, by Richard Feachem, 1977, Simon & Schuster Prehistoric Scotland, by Richard Feachem and Urho Kekkonen, 1963 A Guide to Prehistoric Scotland, by Richard Feachem, 1963, Batsford Prehistoric Scotland, by Vere Gordon Childe, 1940, G Bell and Sons The Prehistory of Scotland, by Vere Gordon Childe, 1935, K Paul, Trench, Trubner & co Prehistoric Scotland and Its Place in European Civilization, by Robert Munro, 1899, W Blackwood and sons Scottish Archaeological Research Framework (ScARF) Toghill, Peter, The Geology of Britain, an introduction, Airlife (2000), The Other Orkney Book, Gordon Thomson, Northabout Publishing 1980, Scotland Before History, Stuart Piggott, Edinburgh University Press 1982, Scotland's Hidden History, Ian Armit, Tempus (in association with Historic Scotland) 1998, External links ScottishGeology.com Scotland's Past BBC - History - Britain's Oldest House? A Journey into the Stone Age History Scotland Magazine: First Settlers - Sand The Megalithic Portal and Megalith Map: Rubbish dump reveals time-capsule of Scotland's earliest settlements The National Trust for Scotland - Press Releases - Archaeological find at Mar Lodge Estate Scotland