Montezuma's revenge is a colloquialism for the stomach discomfort that is contracted in Latin American countries by visitors. The term originates from the conquering of local people by European countries. Montezuma II was Emperor of Mexico from 1502 to 1520 and was in power when the Spanish began their conquest of the Aztec Empire. The discomfort is thought to be the revenge of the local gods that were worshiped prior to the countries becoming Christianized. It is a bacterial illness, always uncomfortable, and occasionally serious. Most cases are caused by the E. coli bacterium.