We first noticed padlocks on bridges when we were in Venice and thought it was odd. After looking it up on the Internet we discovered it's from a book that was made into a film. It's meant to be a way of showing your eternal love for each other, you write your initials on the lock, lock it to a bridge and throw the key into the river. It's a bit odd but kind of impressive to see so many on bridges all over the world.

These were on the Eiffel tower and there were more on the stairs.