It’s almost impossible to visit Prague and not walk across Charles Bridge, a masterpiece of medieval Bohemian architecture that the city takes pride in. Connecting the Old Town with Prague Castle across the Vltava River, thousands of tourists and locals cross the bridge every day.

The majority of the pedestrians, however, do not notice the relief at the Old Town end of Charles Bridge that played an important role in the Middle Ages. Known as the Bradáč, or the “Bearded Man,” the small stone head juts out of the riverfront wall with a frown on his face. It served as a flood warning marker, and it is said that if the water reached his beard it was a sign to evacuate the Old Town.

The Bradáč is a remnant from the days of Judith Bridge, the 12th-century predecessor to Charles Bridge which was destroyed by a flood in 1342. Since then, the relief has seen the Vltava flood countless times. The most disastrous ones took place in 1432 and 1862, and the river water is known to have risen over eight feet above the marker during the 2002 Elbe flood.