All Saints' Day, 9:40 AM
The Lisbon earthquake struck on All Saints' Day 1755, when most of the city's population was in church. Estimated at magnitude 8.5–9.0, it was one of the deadliest in European history. Three shocks were followed by a tsunami and then fires that burned for five days. Around 40,000 people died.
The Marquês de Pombal and the rebuilt city
Prime Minister Sebastião José de Carvalho e Melo (later Marquês de Pombal) organized the response and directed the city's rebuilding. His grid plan for Baixa — the downtown district — became one of the first examples of modern urban planning in Europe. Buildings were designed to be earthquake-resistant using a timber 'pombalino' cage structure.
The philosophical aftershock
The earthquake devastated Leibniz's 'best of all possible worlds' optimism across Europe. Voltaire wrote Candide partly in response — satirizing the idea that everything happens for a reason. The earthquake accelerated Enlightenment skepticism toward both divine providence and metaphysical certainty.