Archaeological artifacts and clues can be destroyed in a number of ways. Nature can destroy a clue by growing over it, eroding it, burying it underwater, or by bacteria eating away at it. People also contribute to the loss of artifacts by robbing them or destroying them in a war. For instance, a Spanish priest destroyed most of the Mayan written records when trying (unsuccessfully) to convert the Mayan people to Christianity. On the other hand, clues can be preserved in extreme climates and conditions where bacteria can't survive as well. Many artifacts have been found in tact in hot and dry climates, very cold climates, very acidic, or very moist environments. Volcanic ash can also preserve artifacts as in Pompeii. Humans can also contribute to the preservation of artifacts when they build structures to protect them or preserve them like they did with mummies. Archaeologists often work to preserve the artifacts they have collected by controlling the environment they are stored in, or treating them and coating them with special chemicals.