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Evil upon the Earth

Modern seismology resulted from the big 1755 earthquake that destroyed Lisbon

Triste tableau des effects causés par le tremblement de terre et incendies arrivés a Lisbonne le 1er Novembre 1755 (Sad picture of the effects caused by the earthquake and fires in Lisbon on November 1, 1755), 1792, unknown author. Museu da Cidade, LisbonA copper etching shows the tents of earthquake refugees, on the outskirts of LisbonTriste tableau des effects causés par le tremblement de terre et incendies arrivés a Lisbonne le 1er Novembre 1755 (Sad picture of the effects caused by the earthquake and fires in Lisbon on November 1, 1755), 1792, unknown author. Museu da Cidade, Lisbon

As in war, a great natural catastrophe brings destruction, death, disease, illness, hunger and fear. In the wake of such misfortune, however, it is common for useful technological and scientific advances to occur. The earthquake that destroyed Lisbon in 1755 had huge repercussions on the political, economic and cultural fate of Portugal. In the scientific field, it resulted in the first studies on the origin and the scope of the effects of earthquakes and in the development of anti-earthquake engineering used in the reconstruction of the Portuguese capital. All the initiatives were led by the secretary of state Sebastião José de Carvalho e Melo, the future Marquis of Pombal and holder of absolute power, as granted by King Dom José I.

The Lisbon earthquake occurred on November 1, All Saints Day, shortly after 09:30. Two or three shocks were preceded by a loud bang in a period of about seven minutes. As it was a holiday, much of the population was at church or at home. In both places the lighted candles and stoves led to major fires immediately after the earthquake, as houses, palaces, churches and public buildings collapsed. Terrified, the survivors rushed to the banks of the Tagus River, which flows through Lisbon, but had no luck: about 30 minutes later, a tsunami with waves of six to nine meters destroyed the port, flooded the lower part of the city and killed many of those who had survived the collapsing buildings and fire.

The exact number of deaths is unknown. Estimates range from 10 thousand to 30 thousand people, based on many reports of the time. It is also unclear how big Lisbon’s population was at the time; perhaps around 200 thousand residents.

Lisbon was not the only affected city. There were deaths plus destruction in other towns near the capital, in the South of the country, on islands, in Spain and in Northern Africa. The epicenter was at sea. The earthquake is now believed to have reached between 8.5 and 9 on the Richter scale.


Carvalho e Melo was responsible for relief management and reconstruction in the wake of the tragedy. His phrase “to take care of the living, to bury the dead,” marked the beginning of the reaction to the disaster. At the same time, he wanted to understand what had happened and what caused it. Thirteen questions were prepared about the earthquake; it is unclear by whom. These were sent to all parish priests in the country, who were required to respond. The questions were simple, such as: What time did the earthquake begin? How long did it last? How many houses were ruined in each parish? How many people died in each room? What was the tsunami like (how tall were the waves and how did the tides flow in and out)?

“The questions were very straightforward and were devoid of the superstitions of the time. They are similar to what we would ask today,” says Igor Pacca, a researcher at the Institute of Astronomy, Geophysics and Atmospheric Sciences at the University of São Paulo (Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo – IAG-USP), who studied the earthquake of 1755. Commenting on the Inquérito do Marquês de Pombal (Survey of the Marquis of Pombal), as the document became known, the famous French seismologist Montessus of Ballore said, “It has a truly scientific character, quite unusual for its time.” He considered it as marking the birth of modern seismology.

There was also innovation in the reconstruction of Lisbon. The engineer Manuel da Maia and architects Eugênio dos Santos and the Hungarian Carlos Mardel, all military men, finished demolishing the lower part of the city and used the rubble to level the ground. They built wider streets and lower buildings. The new buildings employed the “Cage” technique, with locks and diagonal wooden beams, covered by masonry walls (see above). This structure gave the building elasticity and supported the upper floors if the masonry collapsed. The technique lasted until the early twentieth century. “It was a good, early, anti-seismic engineering solution,” says Igor Pacca. Before the Portuguese, the Chinese, in 132 BC, had created an ingenious device to discover from which direction earthquakes came. This ancestor of the seismograph was developed after a major earthquake in China.