Santiago had waited all year for this night. The Immaculate Conception drew the faithful in their finest, and the Compañía was among the city's grandest churches, its walls hung with fabric and its altar lit like a constellation. Worshippers crowded shoulder to shoulder, women filling the nave while men sat apart, separated by an iron grating. The light that made the evening beautiful was also the danger no one had reckoned with. So much open flame, so close to so much cloth and timber, needed only a single careless moment to turn devotion into catastrophe.

An oil lamp near the top of the altar ignited the veils on the wall. Someone tried to beat the flames out with another cloth and only spread them, and the fire leapt from veil to veil and climbed into the wooden roof. The grand decorations that had drawn admiring eyes all evening became fuel. What had been a place of light filled with smoke, and the congregation rose as one to flee. The church's tragic flaw revealed itself in that instant: its doors opened inward, and several side doors had been shut to fit more people inside, funneling the entire crowd toward a single way out.

Between two and three thousand people died that night, most of them women, in what remains one of the deadliest single-building fires in history. The wide hoop skirts of the era turned escape into a trap, snagging and toppling those at the front so that others fell over them, until a wall of bodies sealed the main entrance against both escape and rescue. Many of the men who had reached safety turned back into the flames to pull others out. Around ten o'clock the wooden tower collapsed inward. These were neighbors, mothers, daughters, and sisters, the heart of a city's parish, and Santiago would carry the absence for generations. The grief was so vast that newspapers as far away as Australia struggled to convey it.

Out of the loss came a determination that it never happen again. One of the things Santiago had lacked was an organized fire brigade, and within twelve days José Luis Claro y Cruz founded the city's first volunteer firefighters' corps on 20 December 1863. To this day, Chile's firefighters serve as unpaid volunteers, a tradition born from this night. New safety regulations followed, and the tragedy nudged the country toward separating church and state in the decades after. The church was never rebuilt; its garden and a memorial statue survive in the gardens of the former National Congress. A bell from the church, recovered and later returned from Wales in 2010, hangs as a memorial, and in 2013 metro workers uncovered part of the old foundation, which some in Santiago hope to preserve so the city never forgets the people lost here.