When suicides are dredged from the Seine, it is said, the lovers and the debtors are easy to tell apart: the lovers have paint under their nails, from trying to claw their way back on to the bridge at the last moment, whereas the debtors sink like stones.

ECONOMIST: Bagehot

Most observers date the phenomenon to an Italian teen novel titled "I Want You, " published in 2006, featuring two Roman lovers who immortalized their bond on a bridge in the Eternal City and threw the key in the Tiber.

WSJ: Couples Adorn Bridges With Weighty Tokens of the Heart