Ponte Milvio, Rome.

In late 2006, the bridge began attracting couples, who use a lamppost on the bridge to hang padlocks as a sign of their love.
The ritual involves the couple locking the padlock to the lamppost, then throwing the key behind them into the Tiber.
The ritual was invented by author Federico Moccia for his popular book and movie 'I Want You'.
Similar 'locks of love' traditions have appeared in other places in Italy and Europe.