Talk about secrets of the crypt: Two newly discovered species of bacteria have been found on the walls of ancient Roman tombs.

Bacteria often grow on the walls of underground tombs, causing decay and damaging these archaeological sites. Scientists in Italy found the two new microbes while studying decayed surfaces in the Catacombs of Saint Callistus in Rome.

The Catacombs of Saint Callistus are part of a massive underground graveyard that covers 37 acres. The tombs, named after Pope Saint Callistus I, were built at the end of the second century. More than 30 popes and martyrs are buried in the catacombs.

The new bacteria, part of the Kribbella genus first discovered in 1999, were isolated from whitish-gray patinas, or coatings, on surfaces in the catacombs. They have been named Kribbella catacumbae and Kribbella sancticallisti.

The discovery is detailed in the September issue of the International Journal of Systematic and Evolutionary Mircobiology.

By studying the bacteria, researchers hope to develop ways to keep the microbes from destroying the catacombs and other heritage sites.