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Great Serpent Mound
http://www.atlasobscura.com/places/the-great-serpent-mound
http://indiancountrytodaymedianetwork.com/2014/08/07/rethinking-ohios-history-serpent-mound-older-some-its-dirt-156268
http://www.metmuseum.org/toah/hd/serp/hd_serp.htm
http://www.greatserpentmound.com/
https://www.khanacademy.org/humanities/art-americas/early-cultures/moundbuilders/a/fort-ancient-culture-great-serpent-mound
https://www.ohiohistory.org/visit/museum-and-site-locator/serpent-mound