IMI, National Geographic and the Great Cathedral Mystery Words: Bronzella Cleveland The International Masonry Institute (IMI) National Training Director Robert Arnold, along with other IMI staff, were sponsored by National Geographic to help construct a scaled down version of Brunelleschi's Dome in Florence, Italy for a program on the engineering of the world's largest brick dome. "NOVA's Great Cathedral Mystery," produced by National Geographic Television in association with Camera One Productions, premieres on PBS Feb. 12, 2014. See a preview of the program below.