What destroyed Lisbon in 1755 and changed European thought?

An earthquake on the morning of 1 November - All Saints' Day - followed by fire and then a tsunami up the Tagus. Perhaps a third of the city's buildings came down, tens of thousands died, and the churches, full for the feast day, were among the worst places to be.

The timing did enormous intellectual damage. It was very hard to read a catastrophe that killed the devout at Mass, on a holy day, while leaving parts of the red-light district standing, as considered divine judgement. Voltaire wrote a poem attacking the doctrine that everything happens for the best and then Candide, and Rousseau replied that people had chosen to build seven storeys high in a known quake zone. The exchange is often given as the moment European thought started treating disaster as a problem of physics and planning rather than of sin.

The rebuilding matched it. The Marquis of Pombal sent out a questionnaire to every parish asking how long the shaking lasted, which way it ran, and how the water behaved - the first systematic survey of an earthquake anywhere, which is why he is regarded as a founder of seismology. The new downtown was laid out on a grid with timber cages inside the masonry designed to flex, tested by having troops march around scale models, and is one of the earliest examples of deliberately earthquake-resistant construction in Europe.