Eternal flame
An eternal flame is a fire designed or occurring to burn continuously for an indefinite duration, fueled either by natural emissions of hydrocarbon gases from underground seeps or by artificial supplies of piped natural gas, frequently employed in memorials, religious sites, and symbolic installations to evoke themes of enduring memory, resilience, or sanctity.[1][2] Natural eternal flames arise from geological processes where methane or other combustible gases escape through rock fissures and ignite spontaneously via lightning or human intervention, sustaining combustion autonomously for potentially millennia without maintenance, as observed in sites like Eternal Flame Falls in New York State, where gas seeps from shale formations behind a small waterfall to produce a persistent 8-inch-high flame.[1][3][4] In contrast, man-made eternal flames predominate in commemorative contexts, such as those at national war memorials including the Tomb of the Unknown Soldier in Moscow or the Arc de Triomphe in Paris, where they are ceremonially ignited using controlled gas feeds to symbolize perpetual national gratitude toward fallen soldiers and the unyielding spirit of sacrifice.[5][6] These installations, often encased in protective structures, require ongoing tending to prevent extinguishment from weather or mechanical failure, underscoring their reliance on human intent to achieve symbolic immortality.[4]