The pyramid remained the tallest man-made structure in the world for over 3,800 years,[8] unsurpassed until the 160-metre-tall (520 ft) spire of Lincoln Cathedral was completed c. 1300. The accuracy of the pyramid's workmanship is such that the four sides of the base have an average error of only 58 millimetres in length.[9] The base is horizontal and flat to within ±15 mm (0.6 in)