The size of the mean, spherical Earth, was known by the ancient world to be radius = (7 times 12^6) and circumference (44 times 12^6), evidently using pi as 22/7, the simplest and best pi approximation. It appears the mean Earth was considered sacred and the perimeters of monuments, temples and other sacred places, including landforms, were scaled down versions of these two lengths - most especially factoring 3168 = 288 x 11. [see John Michell, Dimensions of Paradise]. Half of the mean Earth circumference was used as the length of the Meridian equalling 12960 geographical Greek miles. By the time of the Parthenon, the actual meridian length had been measured so that its north-south dimension was one second of the meridian equal to 90 x 9/8 feet = 101.25 which is 100 feet of 81/80 = 1.0125 feet [see my Harmonic Origins of the World, 72-78]. If the earth was perfectly spherical then its degrees of latitude would all be of equal length, as if it did not spin. The degree 51-52 degrees (where Stonehenge and Avebury were located, in Southern England) has that degree length and the Mean Earth appears to have defined the notion of spiritual space for ancient human settlements by using an exact number symbolism of using lengths exactly related to the mean earth though lesser in scale.