Ah, Geneva — a place where you can stroll along the lakefront, gaze at Mont Blanc and, according to scientists, be bowled over by a giant tsunami.

Researchers say they’ve found good evidence that it has happened before. In the sixth century — the age of King Arthur, Mohammed and the bubonic plague — a bishop named Gregory of Tours noted an unusual event in Geneva. In 563, he wrote, a cascade of rocks plunged into the Rhone River, generating a wave of water that “overwhelmed with a sudden and violent flood all that was on the banks as far as the city of Geneva,” over 40 miles away, according to the New York Times.