SERPENT MOUND
LOCUST GROVE, OHIO
The largest effigy mound in North America is the Serpent Mound near Locust Grove, Ohio.  It is a quarter mile long, 4 to 6 feet high and up to 20 feet wide in places.  Recent radioactive carbon datings (1991) have produced dates that averaged 1070 A.D.  Another prominent effigy mound in Ohio, the Alligator Mound has had radioactive carbon datings done in 1999 yielding dates between 1170 A.D. to 1270 A.D.  The dominant culture at the time was the Fort Ancient Culture.  Adena Burial Mounds in the immediate vicinity made people initially think the Serpent Mound was much older.  Credit for the Serpent Mound existing today goes to Frederick Ward Putnam of the Peabody Museum at Harvard University.  He secured it's purchase, and excavated and restored the site from 1886 to 1889.  It is a magnificent structure that is best viewed from the air, or a tower near the end of the tail.  The effigy mound also has astronomical alignments, as shown below.  Why was it constructed? 
We don't really know.  An act of faith perhaps.  Or a demonstration of worship. 
Maybe a gift to the gods above, who could view it better than any mortal on the ground.
My favorite explanation?
A tribute to life, using a serpent to symbolize immortality.
There is much debate about what is in the Serpent's mouth.  Some people have theories due to astronomical phenomena that occured close to radioactive carbon datings of 1070 A.D.  There was an excellent pass by Halley's comet in 1066 and a supernova in 1054 which leads to theories saying the Serpent is chasing a supernova or a comet.  There is also the idea that the oval represents the eye of the Serpent, presented in a highly stylized fashion.  My favorite explanation? The oval shape is an egg and is a symbol of life.
Due to uneven ground (the center of the Serpent is lower than the tail and head), and trees blocking the horizon, viewing solar alignments is far from ideal. Having been there at the solstice, I can tell you this from personal experience.  In fact, you would have to be about 100 feet above ground to get a really good view of a rising or setting sun.
I believe that the alignments are symbolic.    
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