Why am I here now? Well, gather around, children!
In 1575, Venice was ravaged by the plague. Despite all the measures taken, there were no signs of it letting up and so the people resorted to bribery and promised they would build a great church if the lord would lift the torment. And indeed, in 1576, a quarter of the population dead, the plague finally subsided.
Keeping word, the city commissioned a church to be built on the island of Giudecca overlooking the lagoon. The cornerstone was laid in 1577 and a temporary bridge was erected so the doge could lead a procession to the new church.
The procession was repeated every year since on the third Sunday of July as the Festa del Redentore, the Feast of the Redeemer. The bridge is erected again every year.