Answer: Padlocks

Normally when you think of damage to a bridge you think of earthquakes, trucks with high-tonnage payloads, or other large and energetic things. But padlocks? How many padlocks does it take to damage a bridge? How about 700,000?

In Paris there is a pedestrian bridge known as Pont des Arts that crosses the River Seine and links the Institut De France with the central square of the Palais du Louvre. There is a tradition, and we use that term loosely because there is no record of the tradition prior to 2008, of attaching padlocks to the bridge. Couples will write or etch their names onto a padlock, affix the lock to the safety rails and fencing on the bridge, and then throw the key into the river as a symbol of their commitment to each other.

Romantic gestures are all well and good, but this particular gesture is outright dangerous. The practice has added a load of over 60+ metric tons to the bridge and in the summer of 2014 a section of the guard rail and fencing collapsed under the weight of the locks attached to it. Fortunately, the section collapsed inwards onto the bridge surface and not outwards and down into the heavily traveled river where it could have easily injured or killed a passenger on the river’s numerous tour boats.

The city has since began removing locks from both the Pont des Arts and other bridges defaced in such a fashion as well as considering banning the practice to protect the bridges and other historic locations in Paris.