Partly built starting in 1145, and then reconstructed over a 26-year period after the fire of 1194, Chartres Cathedral marks the high point of French Gothic art. The vast nave, in pure ogival style, the porches adorned with fine sculptures from the middle of the 12th century, and the magnificent 12th- and 13th-century stained-glass windows, all in remarkable condition, combine to make it a masterpiece. The massive weight of its high clerestory windows meant that flying buttresses — external supports — had to be used in new ways. Each curved pier connects with an arch to a wall and extends (or ‘flies’) to the ground or a pier some distance away. Built of limestone, Chartres is 34 meters high and is 130 meters long.