Reconstructing the cause and origin of structural fires in the archaeological record of the Greater Southwest (Mexico, New Mexico)

James R. Lally
Department of Anthropology, The University of New Mexico
June, 2005


Archaeologists frequently assume ancient structural fires are intentional incendiary fires. This assumption has become a foundation for behavioral arguments suggesting motives for these supposed intentional fires. The basic assumption that most, if not all ancient structural fires were intentional has not been subjected to rigorous testing. In this research principles of fire science, arson investigation and fire protection engineering, including mathematical computer fire modeling, were applied to the archaeological record of the Greater Southwest. This was done to determine if ancient structural fires were providential, accidental or intentional incendiary fires. Prehistoric sites in Chihuahua and New Mexico were excavated to obtain artifacts and other evidence of fire. A full scale model of a prehistoric room was constructed. After a fire in this room was modeled using a mathematical computer fire modeling program, it was then filled with fuel and burned. This experience, as well as a basic understanding of the chemistry, physics and behavior of fire, was applied to the prehistoric structures that were excavated in Chihuahua and New Mexico. Standards were articulated by which ancient structural fires could be classified as providential, accidental or incendiary. These standards were applied to the excavated sites. Considerations of the room size, construction material, configuration, use and expected fuel load were compared to the physical evidence that was recovered from the ancient structural fires. A prehistoric room fire in Chihuahua was determined to be accidental. An ancient structural fire in New Mexico was classified as being an incendiary fire. The motives behind this intentional fire remain a mystery. Future investigations of structural fires in the archaeological record should take advantage of readily available tools to reach valid conclusions.