The Great Lisbon Earthquake

In the 18th century, Lisbon, the capital and largest city of Portugal, thrived from the influx of diamonds and gold from its Brazilian colony. Housing almost 10% of Portugal’s 3 million residents, Lisbon served as a major Atlantic seaport and an important hub for Catholicism, home to many Catholic religious leaders.

On the All Saints’ Day morning of November 1, 1755, Lisbon was struck by three powerful tremors within three to six minutes. With an epicenter offshore, this catastrophic earthquake occurred along the major fault line separating Europe from North Africa. It affected not only Portugal but also the broader Iberian Peninsula and Northwest Africa. 

The strongest of these quakes likely reached a magnitude of 8.5-9 on the Richter scale, making it the most powerful earthquake recorded in Europe and northern Africa. However, this is an estimate as no measuring equipment existed then.

Tragically, as numerous Lisbon residents attended mass, many churches crumbled under the seismic force, killing or injuring thousands. The earthquake’s violent shakes demolished large public buildings and about 12,000 homes, creating fissures up to 16 feet (5 meters) wide in the city center. Many people were killed by falling debris, while survivors fled to the seaside, only to witness the ocean’s alarming retreat.

Forty minutes after the earthquake, a tsunami towering 20 feet (6 meters) high swept through the harbor and downtown, claiming the lives of those seeking refuge there. The massive wave also set off extensive fires by toppling homes and churches lit by candles, causing further destruction.

The earthquake and its aftermath claimed the lives of 30,000 to 60,000 people, ranking it among history’s deadliest earthquakes. It destroyed 70% of Lisbon’s structures, erasing much of Portugal’s cultural heritage, including 16th-century Manueline architecture and invaluable historical collections.

King Joseph I of Portugal and the royal family, having left the city earlier that day, survived unharmed. The earthquake, however, left him deeply paranoid, refusing to sleep in walled structures and relocating the royal court to a large tented complex.

Prime Minister Sebastião José de Carvalho e Melo, better known as the Marquis of Pombal, demonstrated exceptional leadership following the earthquake. His response to the immediate crisis was decisive: 

Pombal took swift action, deploying troops to maintain order and organizing volunteer firefighter groups. He made the controversial decision to have bodies buried at sea, using barges for this purpose. While criticized by the Catholic authorities for disregarding traditional burial customs, this move likely prevented further devastation from a potential plague outbreak.

Reconstruction of Lisbon began promptly. Chief Engineer Manuel da Maia proposed five plans, one even suggesting abandoning the city. However, the Marquis of Pombal chose to rebuild, transforming the medieval cityscape into one with straight avenues and grand plazas. The new building code introduced innovative features like firewalls and the “Pombalina cage,” a wooden frame designed to withstand earthquakes. The army tested the earthquake resistance of these structures by marching up and down the streets. Additionally, Pombal implemented drainage systems under the streets to prevent flooding.

The new Lisbon was literally built atop its ruins. Modern subway construction has revealed earthquake debris 30 to 50 feet (10 to 15 meters) deep, raising the city’s foundations and potentially safeguarding it against future tsunamis.

The Great Lisbon earthquake played a pivotal role in the birth of seismology. This significant shift towards a scientific understanding of earthquakes began with the Marquis of Pombal’s initiative. He sent a comprehensive questionnaire to parishes across the country, inquiring about specific details of the earthquake, including its timing, the death toll, and whether the sea level rose or fell first. These inquiries laid the foundation for what we know today about earthquakes.

A seismic shift in public perception followed the devastating earthquake. Devout Europeans, deeply shaken by the immense loss of innocent lives, began to doubt their belief in divine retribution. For influential thinkers like Voltaire, the Lisbon earthquake undermined the Catholic Church’s claim to understand the universe, while Immanuel Kant saw it as evidence of the planet’s indifference to human life. Also, Kant, in his essays on the earthquake, offered one of the earliest natural explanations for such disasters. His work represented a pivotal shift towards scientific reasoning, despite his theories being eventually disproven.