The proportions are way off in the below.........they say the Egyptians would do that with a string..........to make triangles...................exploiting the 3 - 4 - 5 right triangle.....................those 3 #'s added together equal......................12..................so u could take a string.................12 units of whatever long.......................and make a triangle out of it.............with a 90 degree angle.............just make one side be 3 units long...........the others would have to be 4 and 5 respectively..............

I drew in the 1/2 crudely............it doesn't match up...........I am conveying the idea..........of the red circle with center at (1/2, 0)..................with a radius of 1/2 unit..............so it would touch the origin at the left..............and (1, 0) at right.................................................2pi r.............is the circumference of a circle.......................................if r = 1/2...............................the trip around the red circle............would be exactly pi.............