It was the most destructive natural disaster in the history of Europe: On November 1, 1755, an earthquake shook the seabed off Lisbon. Buildings collapse in the city, thousands of people die. The survivors flee to the port - and are surprised by a huge tsunami wave. If it hadn't happened on All Saints' Day, the Lisbon catastrophe would certainly not have been so devastating. A large proportion of people perish in the churches where the faithful have just gathered to worship. To this day, no one knows how many actually died from the earthquake. Estimates speak of up to 100,000 dead. The reason for the disaster: off the Portuguese coast, several continental plates are colliding at the bottom of the Atlantic, there is an increased danger of earthquakes - until today. A research team is currently examining the Gulf of Cadiz for traces. The aim is to set up an effective tsunami early warning system.