The locks aren't 'used' as such - what happens is that lovers buy the lock, write their names on it, attach it to the railings, and throw the key into the river.

I guess it's a way of saying 'together for ever'...

The locks form interesting patterns... nice shot!
I saw a bunch of locks on a bridge to Ortigia in Siracusa but didn't realize the "lovers" significance... How are they used? I assumed they were for securing the boats moored there.

Lovers' locks on the Ponte Veccio, Florence.