The Basel earthquake devastated Switzerland

On the night of 18 October 1356, a series of violent tremors shook the city of Basel, in what remains the strongest documented earthquake in Switzerland’s history. The shaking began earlier in the day and built through the evening, with the main shock striking around 22:00 local time. Modern estimates place its moment magnitude near 6.6, with the most damaging studies ranging as high as 6.9–7.1.

The quake destroyed much of Basel and shattered castles and churches across a wide radius of the surrounding countryside. Its effects were felt across a vast region stretching, by some accounts, from Paris to Prague.

The same earthquake today could kill thousands and cause tens of billions of francs in damage.

The culprit lies underground: Basel sits near the southern end of the Upper Rhine Graben, an ancient rift system whose active normal faults still slip today. Because foreshocks drove many residents out of buildings before the main shock, the medieval death toll is thought to have been relatively low, even as the city itself lay in ruins.