We have a trip to the Newark Earthworks planned for April of this year...  I am attaching a video that is really informative, and I am really looking forward to the trip.

Information from the Newark Earthworks website state that the Newark Earthworks are the largest set of geometric earthen enclosures in the world. Already a National Historic Landmark, in 2006, the State of Ohio designated the Newark Earthworks as "the official prehistoric monument of the state." 

The Newark Earthworks were built by people of the ancient Hopewell Culture between 100 B.C. and 500 A.D., this architectural wonder of ancient America was part cathedral, part cemetery and part astronomical observatory. The entire Newark Earthworks originally encompassed more than four square miles. Over the years, the growth of the city of Newark destroyed many of the Newark Earthworks, but three major segments survived because of the efforts of interested local citizens:

Great Circle Earthworks: Formerly known as Moundbuilders State Memorial, the Great Circle Earthworks is nearly 1,200 feet in diameter and was likely used as a vast ceremonial center by its builders. The 8 feet (2.4 m) high walls surround a 5 feet (1.5 m) deep moat, except at the entrance where the dimensions are even greater and more impressive.

Octagon Earthworks: Enclosing 50 acres, the Octagon Earthworks has eight walls, each measuring about 550 feet long and from five to six feet in height. The Octagon Earthworks are joined by parallel walls to a circular embankment enclosing 20 acres. 

Wright Earthworks: This earthwork consists of a fragment of a geometrically near-perfect square enclosure and part of one wall that originally formed a set of parallel embankments, which led from the square to a large oval enclosure. Originally, the sides of the Newark square ranged from about 940 to 950 feet in length, and they enclosed a total area of about 20 acres.

While we can never know with any certainty the Hopewells' purpose in designing the earthworks, one theory is that the Hopewell built these earthworks on such a massive scale for astronomical accuracy—long, straight embankments provide longer sight lines that increase the accuracy of astronomical alignments. In 1982, professors Ray Hively and Robert Horn of Earlham College in Indiana discovered that the Hopewell builders aligned these earthworks to the complicated cycle of risings and settings of the moon. They recovered a remarkable wealth of indigenous knowledge relating to geometry and astronomy encoded in the design of these earthworks. The Octagon Earthworks, in particular, are aligned to the four moonrises and four moonsets that mark the limits of a complicated 18.6-year-long cycle.