Parisian Sinkholes Revealed City Built on Nothing

Homes, people, and streets were swallowed up by sinkholes in the 18th century, so architect Charles-Axel Guillaumot fearlessly led a team in mapping and reinforcing the weak foundations of Paris. The tunnels that once terrorized Parisians became a sacred site as they were dedicated as catacombs. Guest: Ian Boyd, PhD candidate in the French section of Modern & Medieval Languages and Linguistics at Cambridge