An eternal flame is a flame, lamp or torch that burns for an indefinite time. Most eternal flames are ignited and tended intentionally. However, some are natural phenomena caused by natural gas leaks, peat fires and coal seam fires, all of which can be initially ignited by lightning, piezoelectricity or human activity, some of which have burned for hundreds or thousands of years. In ancient times, eternal flames were fueled by wood or olive oil; modern examples usually use a piped supply of propane or natural gas.
