Revolutionizing.

If its beauty and magnificence is instantly apparent, so much about Notre Dame is not. To begin with, we don't know who built this cathedral—or how. 

The bishop of Paris, Maurice de Sully, commissioned the massive church complex around 1160. Yet the names of those who first constructed this masterpiece are lost to history. They left no records—only centuries of speculation—behind.

"So much ink has been spilled over that building," says art historian Andrew Tallon. "So much of it is completely wrong."

A former composer, would-be monk, and self-described gearhead—or, as he puts it, "tacklehead"—Tallon intends to make that history right. With the help of 21st-century laser scanners, he is teasing out clues hidden in the ancient stones of Notre Dame and other medieval structures—and revolutionizing our understanding of how these spectacular buildings were made.

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