National Geographic Television

The 15th-century dome at the cathedral of Santa Maria del Fiore looms over the city of Florence, Italy. Designed by Filippo Brunelleschi, the dome is still the biggest one built with masonry in the world.

A hour-long documentary by NOVA and National Geographic Television, "Great Cathedral Mystery," investigates how Brunelleschi managed to design the construction of the dome, without the use of a wooden support structure, more than 500 years ago. The risks are obvious. A dome slopes inward, so a miscalculated design could cave in during construction, taking the bricklayers with it.

The documentary profiles the particularly curious Massimo Ricci, an architecture and engineering professor at the University of Florence, who decided that the only way to figure out how the structure was built was to try it out himself, with a much smaller model in a Florence park. Tucked into the parallel storylines of the Ricci and Brunelleschi domes, the documentary dives into some early building techniques, such as the herringbone pattern of bricklaying and an oxen-powered cogwheel that lifted building materials up to the top of the cathedral.

The documentary airs tonight on PBS.