The custom is inspired by a book by novelist Federico Moccia in which a couple place a bicycle lock around a lamppost and throw the key into the Tiber.
The gesture was meant to symbolise the couple eternally locking their hearts together.
It took off and clusters of padlocks can be found near other landmarks in other Italian cities.
David Pescovitz is Boing Boing's co-editor/managing partner. He's also a research director at Institute for the Future. On Instagram, he's @pesco.