On November 1, 1755, the sea pulled back from Cascais and came back as a wall of water.
Last reviewed 6 October 2026 · A two-minute read · 3008 BC–2018
The short answer
On 1 November 1755, a tsunami triggered by the Lisbon earthquake struck Cascais, Portugal, after the sea withdrew from the shore and returned as a wall of water, killing more than 300 people and damaging the Citadel of Cascais on what had begun as All Saints' Day.
Paula Rego Museum, Cascais, Portugal. Architect: Eduardo Souto de Moura. — 2009 · Pedro Ribeiro Simões from Lisboa, Portugal · CC BY 2.0
November 1, 1755
A tsunami drowned 300 people after church bells rang
The morning started with church bells, not warnings. November 1 was All Saints' Day, and the town below your feet was full of people at mass. Then the ground moved. The 1755 Lisbon earthquake struck the whole coast at once, and in Cascais the Citadel of Cascais took heavy damage within minutes.
What came next was worse. The sea drew back from the shore, far enough to expose stretches of seabed that no one in the town had ever seen bare. Then it returned as a tsunami, driving up through the streets and along the riverside. Boats were wrecked where they sat at anchor. The water killed more than 300 people in Cascais alone, on a town that had been standing in church an hour before.
Nobody counted the bodies with any precision. What survived is the shape of the day: a holy morning, a shaking ground, a retreating sea, and a wave that did not ask who was faithful before it reached them. The citadel was patched up. The town went back to fishing. The sea did not stop taking things from Cascais, before or after.
The sea withdrew far enough to expose the seabed, then came back and killed more than 300 people.
1606
A pepper ship sank off Cascais and lay hidden
A century and a half before the tsunami, the sea had already shown what it could keep. In 1606 a Portuguese ship called the Nossa Senhora dos Mártires shipwreck went down off the coast near Cascais, loaded with pepper and goods carried back from Asia on the spice trade routes. It sank and stayed sunk for nearly four hundred years.
When archaeologists finally excavated the wreck, they found Ming porcelain still packed where it had been stowed, along with navigational astrolabes used to find this coast in the first place. The pepper was long gone. The porcelain and the instruments were not. The same stretch of water that would later drown the town had already taken a cargo ship and its crew, quietly, without an earthquake to explain it.
late 16th or early 17th century
A second wreck carried porcelain, cannons and cowrie shells
The 1606 wreck was not the only one down there. In September 2018, dredging work at the mouth of the Tagus turned up a second ship, this one unnamed, dating to the late 1500s or early 1600s. It carried spices, Chinese porcelain from the Wanli period, bronze cannons stamped with the Portuguese coat of arms, and cowrie shells, the kind used as currency in the slave trade.
1939
Survivors of a sunken freighter reached shore alive
The sea off Cascais was still handling disasters in the twentieth century, though this one ended differently. In September 1939, at the start of World War II, the British freighter British freighter Bosnia was sunk, most likely by enemy action. Its survivors did not drown. A Dutch ship carrying the castaways reached the bay of Cascais, and a tug met it there on September 6, 1939, bringing the survivors ashore.
Where the tsunami and the two wrecked cargo ships left nothing behind but ruin and porcelain, the Bosnia's story ends with people stepping onto the same shore alive. The bay that swallowed ships for four hundred years also, this once, delivered its people back.
The water in front of Cascais still holds more than it has ever given back.
Read the ground you are standing on
Every person, building and event in this story opens into its own dig in the app — and Strata will dig the ground under your feet instead, wherever that is, in about a minute, with every source shown.
Roman-era remains, including ten tanks for salting fish, were discovered along Rua Marques Leal Pancada in Cascais, evidence of a Roman fish-processing works on this ground.
Castilian troops captured and sacked the town of Cascais in 1373, part of repeated conflict and blockades that struck the port through the late 14th century.
The Portuguese carrack Nossa Senhora dos Mártires went down off the coast near Cascais in 1606 carrying pepper and Asian trade goods, and excavation of the wreck later recovered Ming porcelain and astrolabes.
On 1 November 1755 an earthquake struck Lisbon, and the sea withdrew from Cascais before returning as a tsunami that wrecked boats, tore through the streets and riverside, and killed more than 300 people in the town.
Dredging at the mouth of the Tagus in September 2018 turned up a late-16th or early-17th century Portuguese ship carrying spices, Wanli-period Chinese porcelain, bronze cannons bearing the Portuguese coat of arms, and cowrie shells used in the slave trade.
The British freighter Bosnia was sunk in September 1939, likely by enemy action at the start of World War II, and survivors reached Cascais bay by 6 September aboard a Dutch ship met by a tug.
An earthquake struck the coast, the sea withdrew from Cascais exposing bare seabed, and then returned as a tsunami that wrecked boats, tore through the streets and riverside, damaged the Citadel of Cascais, and killed more than 300 people in the town.
What was here before the 1755 tsunami?
The town of Cascais was full of people attending All Saints' Day mass when the earthquake struck, an hour before the sea returned as a wave.
What ships sank off the coast near Cascais?
The Portuguese carrack Nossa Senhora dos Mártires sank in 1606 carrying pepper and Asian trade goods, later yielding Ming porcelain and astrolabes, and a separate late-16th or early-17th century Portuguese ship was found in 2018 carrying spices, Wanli porcelain, bronze cannons and cowrie shells.
What happened to the British freighter Bosnia near Cascais?
The Bosnia was sunk in September 1939, likely by enemy action at the start of World War II, and its survivors reached Cascais bay on 6 September aboard a Dutch ship met by a tug, arriving alive.
Was the Citadel of Cascais damaged in the 1755 earthquake?
Yes, the Citadel of Cascais took heavy damage within minutes of the earthquake striking, before the tsunami that followed.
