Evidence of historic use of the concepts of perimeter and circumference goes back to the ancient Egyptians and Babylonians in about 1800 B.C.E. The pyramids are built to exact mathematical formulae although there is no written record of the use of Pi, a dimension of calculating circumference, in the archaeological data. Clay tablets from Babylonia describe the complex math used in building the elaborate canal system used for transportation and irrigation. Archimedes is credited with the formal discovery of Pi in 240 B.C.E. in Greece, and Eratosthenes was the first person to calculate the circumference of the earth accurately, sometime between 276 and 195 B.C.E. Liu Hui of China and Aryhabata of India were working with Pi long before the Greeks wrote about it.