On November 1, 1755, a massive earthquake hit Lisbon during morning Mass on All Saints' Day. Churches were full. Candles lit for the holiday toppled and started fires that joined the shaking and the sea.
The quake struck just after 9:30 in the morning. Witnesses said the ground moved for three to six minutes. A tsunami followed, dragging the harbor's water out and then rolling back in. Much of the city fell.
The king survived. The prime minister acted. He kept order.
The disaster killed an estimated 40,000 to 60,000 people in a city of about 200,000, and the toll forced a question that philosophers could not avoid: why would a merciful God let this happen to faithful worshippers at prayer on a holy day. The Marquis de Pombal, the king's chief minister, ordered ruins cleared, tents raised for the homeless, and looters hanged, then rebuilt Lisbon on a grid with widened streets built to survive the next shock.
The event reached far beyond Portugal. Voltaire wrote about it, and thinkers began to treat earthquakes as natural facts to be measured rather than signs to be read. Lisbon never looked the same, and the study of disaster gained a science it had lacked before the morning it broke.