Chile sits on one of the most violent seams on Earth. Just off its coast, the Nazca plate grinds beneath the South American plate along a convergent boundary, and the strain it stores is released in some of the largest earthquakes the planet produces. The 1647 disaster was felt across a vast stretch of land, with extreme ground motion reported between the Choapa and Maule rivers, though the documented destruction was concentrated on Santiago itself. Scientists still debate which fault ruptured - no clear evidence points to the San Ramón Fault that runs along the city's eastern edge, leaving other faults of the West Andean belt as candidates. By the scale of its damage, the event likely reached a magnitude near 8.0, comparable to the great Valparaíso earthquake of 1906. No tsunami followed.

Inside the ruined Iglesia San Agustín, something survived that the city would never forget. A carved figure of Christ, the Cristo de Mayo, was pulled intact from the debris - all except its crown of thorns, which had slipped down to rest against the figure's neck. What struck the survivors was the detail: the crown's inner diameter was smaller than the head it had somehow fallen past. To a terrified population, it read as a sign. Gaspar de Villarroel, the Bishop of Santiago, salvaged the image himself and carried it through the wreckage to the Plaza de Armas, holding it up before the crowds gathered there in the dark. Each year since, on 13 May, people of Santiago have gathered to remember the night and the crucifix that came through it.

The earthquake was only the first blow. Days later, heavy rains swept the broken city, and water pooling in the rubble fouled what little sanitation remained. Out of that misery came an epidemic the survivors called chabalongo - the period's name for typhus. Over the following weeks it killed an estimated two thousand people, twice the toll of the quake itself. The disaster's full reach was measured not in the seconds of shaking but in the slow weeks of fever and burial that followed. For many families, the building that collapsed was the lesser tragedy.

So thorough was the destruction that the colonial government debated abandoning the site entirely, moving the capital a few kilometers north to the area now called Quillota. In the end they chose to stay and rebuild Santiago where it stood, on the same fault-shadowed ground. Bishop Villarroel offered the survivors something gentler than the era usually allowed. The earthquake, he insisted, should not be read as divine punishment - it would be a mortal sin, he said, to judge that the citizens' sins had destroyed their city. The night entered literature too: in 1807 the German writer Heinrich von Kleist set his haunting novella The Earthquake in Chile against this very catastrophe, carrying the memory of 1647 across an ocean and a century and a half.