On a trip to this thrumming city about 15 years ago, art historian Michael Stoughton hoped to visit a famous Baroque church in the Sanita neighborhood. An Italian friend said no — the area was too dangerous. If you must, the friend added, then take a taxi and make the driver wait for you.

Today that same neighborhood attracts thousands of tourists every year, drawn by the lovely basilica, the Santa Maria della Sanita, and two nearby catacombs that are among the most remarkable in Europe.