This 2019 episode notes that the Catacombs contain the bones of an estimated 6 to 7 million people, and explains that their history is really two interconnected stories of mines and human remains.

Robert Moses and the Shaping of New York, Part 1
41:59

SYMHC Classics: Eradication of Smallpox
43:25

Behind the Scenes Minis: Progressive Medicine
22:11