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Thucydides, Book I, chap. II.
Strabo, Book II, chap. III, 7.
McGee and Thomas, Prehistoric North America, pp. 408-414, Vol. XIX of History of North America, edited by T.N. Thorpe. Philadelphia, 1905.
Hodgkin, Italy and Her Invaders, Vol. II, p. 214. Oxford, 1892.
Sir John Lubbock, Prehistoric Times, p. 587. New York, 1872.
D.G. Brinton, The American Race, pp. 116-119. Philadelphia, 1901.
O.T. Mason, Primitive Travel and Transportation, pp. 249-250. Smithsonian Report, Washington, 1896.
Thucydides, Book I, chap. II.