The Great Pyramid of Khufu at Giza, built about 2700 B.C., is so accurately square and so perfectly oriented to the cardinal points of the compass that it is evident that the Egyptians used surveying as means of controlling construction just as we do today. Surveying also was used to determine property lines, as Sumerian clay tablets (1400 B.C.) show records of land measurement and plans of cities and nearby agricultural areas. Boundary stones marking property corners have been preserved, and there is representation of land measurement of the Menna at Thebes (1400 B.C.) showing two men chaining a wheat field with what appears to be II a cord with knots!) at regular intervals.