Praça do Comércio, Lisbon

Six minutes that ended a golden age

At 09:40 on All Saints' Day, 1 November 1755, an earthquake of magnitude 8.5 to 9.0 struck off the coast of Portugal.

The shaking lasted six minutes — three times longer than the most destructive shaking of the 1906 San Francisco earthquake.

Lisbon, the capital of a Portuguese empire that controlled half the New World's gold output, was reduced to rubble within minutes. Forty minutes later a 6-metre tsunami arrived in the Tagus estuary. By evening, fires from overturned All Saints' Day candles in the city's churches had merged into a five-day firestorm that consumed everything the earthquake had not.

Why the day of the dead

The timing multiplied the casualties. All Saints' Day. The morning of one of the most attended church services in the Catholic calendar.

The city's stone churches, with their tall medieval towers and recently completed Baroque facades, were the first structures to collapse. They collapsed onto packed congregations. Roughly 30 000 to 40 000 people died in Lisbon alone out of a population of perhaps 200 000, and another 10 000 to 30 000 across southern Portugal, Spain, and Morocco.

A philosophical earthquake

The Lisbon earthquake landed in the middle of the European Enlightenment, and it became one of the most argued-about events of the eighteenth century.

Voltaire's Poème sur le désastre de Lisbonne (1756) attacked the Leibnizian doctrine that this is the best of all possible worlds. His Candide (1759) is an extended satire on the same theme. Immanuel Kant published three short treatises on the earthquake.

The disaster contributed materially to the European secular shift. If a benevolent God had designed the world, why had He arranged for tens of thousands of pious Catholics to be killed at Mass on a holy day?

Pombal's reconstruction

The Prime Minister Sebastião José de Carvalho e Melo, the Marquês de Pombal, rebuilt central Lisbon on a strict grid plan with identical neoclassical facades, wide streets, and earthquake- resistant construction techniques he invented for the rebuild.

The gaiola pombalina — the "Pombaline cage" — was a flexible wooden lattice frame inside stone walls designed to oscillate during seismic shaking rather than collapse. Test models were built in fields outside the city and troops marched in formation around them to simulate earthquake vibrations.

The Pombaline reconstruction is the modern Baixa district. The area of central Lisbon that tourists visit today. The world's first deliberately earthquake-engineered urban district.