Area of a Circle

You are to solve the mathematical mystery of these ancient structures.  You must design a paper that contains the mathematical characteristics (radius,diameter, circumference, and area), other important details (location,important dates, etc.), and complexity of the construction that pertain to these structures.  You must postulate a opinion on how do you think ancient people built these structures with such mathematical precision having little or no math background. 

Your can find all the information that you need using the following search engines such as: Google, FireFox, and/or Bing.