The Catacombs of Paris are a network of subterranean tunnels and rooms located in Roman-era limestone quarries that were converted into a mass tomb at the end of the 18th century to curb the spread of disease due to improper burials and mass graves. Today, only a small portion of the catacombs, which span more than 186 miles, is open to the public, but many enter them illegally via secret entrances found throughout Paris. Why were the catacombs closed to the public in 2009? Discuss