For centuries, Parisians had buried their dead in the Cemetery of the Innocents. By the 18th century, the grounds had become overcrowded — spewing foul odors across the city. Residents worried that it posed a public health threat, and petitioned the government for a solution. But where could they move millions of remains? Stephanie H. Smith explores the vast, underground network of the Catacombs. Lesson by Stephanie H. Smith, directed by Laura Jayne Hod