How Portugal’s Biggest Disaster Launched a Scientific Discipline

Why you should care

Because a 1755 quake shook thinkers and movers into serious action.

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Geo facts & figures

Most of the population of Lisbon was in church when the first quake hit. It was the morning of All Saints Day, 1755, and this was the most prominent city in one of the world’s most powerful countries. None of that mattered, of course, when the shaking started.

The Lisbon quake is still a defining moment in the city’s history. Estimated to be an 8.5 magnitude or higher on the modern-day Richter scale, it was followed by two smaller quakes and a tsunami, as high as 15 meters, then by days of fires that engulfed the city. Hundreds of aftershocks happened over subsequent months. No official death count exists, but sources both contemporary and modern estimate somewhere between 10,000 and 60,000 people died (the population numbered about 1 million at the time). About 82 percent of the city’s buildings were destroyed, among them churches, cathedrals, royal palaces and the opera house.

That the rich and the outwardly godly weren’t spared in the quake may have been one factor that spurred what amounted to an existential crisis among some Europeans. While many did turn to religion in the time of crisis — and 18th-century Portugal had its share of spiritual leaders blaming the quake on human sin, a phenomenon that persists today — science and philosophy also had their part to play. Thinkers like Voltaire, Rousseau and Immanuel Kant (there’s more on Kant; keep going) all meditated on the earthquake and what it meant for humankind and its trust in fate.

The scientific quest kicked off in Lisbon 263 years ago still doesn’t have the answer it was truly searching for.

The birth of seismology — the science of earthquakes and their accompanying phenomena — is often traced right back to 1755, and specifically to one man: Sebastião José de Carvalho e Melo, the Marquis of Pombal. Technically serving as Secretary of State to King Joseph I, Pombal took on a much larger role in the aftermath of the quake, explains Mark Molesky, author of This Gulf of Fire: The Destruction of Lisbon, or Apocalypse in the Age of Science and Reason. “The king was kind of shell-shocked — he and his family were almost killed by this,” Molesky says, “and he essentially gave power to Pombal, and Pombal ruled in his name for about 20 years.”

It was Pombal who ordered that a questionnaire about the earthquake be filled out for every district of the city: How many aftershocks? Did the sea rise or fall before the tsunami? Which parts of the city were damaged by fire, and to what extent? That data, still housed in Portugal’s archives, has allowed modern researchers to examine and reconstruct the details of the 1755 quake with the benefit of modern scientific theory.

This is not to say that the scientists of the day were on the right track when it came to the earthquake’s causes. Astronomer John Michell put forth an elaborate theory involving a wave of force, much like a sound wave, perhaps caused by a volcano superheating rock layers in the earth. Immanuel Kant — yes, that one — appropriated ancient theories invented by Aristotle, who thought quakes might be caused by wind passing through underground caverns. Kant, feeling that winds weren’t strong enough to cause such devastation, decided it might be explosions in underground caverns.

Of course, the study of plate tectonics has given us insight into what actually causes earthquakes. But the plot of Dwayne “the Rock” Johnson’s classic San Andreas aside, that knowledge hasn’t actually made quakes easier to predict. Knowledge is power, except when it isn’t: The scientific quest kicked off in Lisbon 263 years ago still doesn’t have the answer it was truly searching for.

Pombal’s contributions didn’t lead to much prevention. But preparation, that he could do. Tasked with rebuilding Lisbon almost from the ground up, Pombal rebuilt many neighborhoods on a system of logical grids in an architectural style still known as Pombaline — notable for being some of the first modern architecture to incorporate anti-seismic safety features, like wooden frames that could sway without breaking. The new buildings, which also used wooden lattice frames meant to evenly distribute the force of a quake, and doors, windows and walls were built to standard sizes. And soldiers were ordered to march heavily around buildings to stress-test them. Note: There hasn’t yet been an opportunity to test this in real life — 1755 remains the biggest earthquake Portugal has ever experienced.

Pombaline Lisbon has been placed on a list of candidates to become a World Heritage site, not just for its now-iconic orderly architectural style, but as a commemoration of Portugal’s contribution to being prepared.

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