Little is known with certainty about the serpent—not even how many thousand years old it is.
A New Multistage Construction Chronology for the Great Serpent Mound, USA, Edward W. Herrmann, G. William Monaghan, William F. Romain, Timothy M. Schilling, Jarrod Burks, Karen L. Leone, Matthew P. Purtill, Alan C. Tonetti, Journal of Archaeological Science, Vol. 50, pp. 117–125, Oct 2014.
Serpent Mound: A Fort Ancient Icon?, Robert V. Fletcher, Terry L. Cameron, Bradley T. Lepper, Dee Anne Wymer and William Pickard, Midcontinental Journal of Archaeology, Vol. 21, No. 1, pp. 105–143, Spring 1996.
The Serpent Mound of Ohio, F.W. Putnam, The Century Illustrated Monthly Magazine, Vol. XXXIX, No. 6, pp. 871–888, April 1890.
History Got it Wrong: Scientists Now Say Serpent Mound as Old as Aristotle by Geoffrey Sea for Indian Country Today, 7 Aug 2014.
Crazy Theories Threaten Serpent Mound, Demean Native Heritage by Mary Annette Pember for Indian Country Today, 6 June 2013.