Carved from a hundred million pounds of stone, soaring effortlessly atop a spider web of masonry, Gothic cathedrals are marvels of human achievement and artistry. But how did medieval builders reach such spectacular heights? Consuming the labor of entire towns, sometimes taking a hundred years to build, these architectural marvels were crafted from just hand tools and stone. Many now teeter on the brink of catastrophic collapse. To save them, an international team of engineers, architects, art historians and computer scientists searches the naves, bays and bell-towers for clues to how the dream of these heavenly temples on earth came true.