NOVA: Building the Great Cathedrals

An examination of how the great medieval cathedrals were built. The architectural marvels, made from stone and by hand, often required the labor of entire towns, and some took 100 years to finish. Many, however, now may collapse. Here, architects, engineers, computer scientists and art historians investigate the secrets used to build them in order to save them, including how the soaring, glass-filled walls where erected.