I was puzzled when I saw this in Venice on Christmas Eve. Was it a tap? A drain for when it floods? No, it's actually a well.
In the past these wells were used by Venetians as their only source of fresh water. The wells were actually cisterns that collected rainwater channelled from rooftops which was then sand-filtered. Almost every courtyard and piazza had its own well. These wells provided water until 1886 when an aqueduct brought water in from nearby mountains.
Venice is still full of these old, weathered wells.
Christmas in Venice is beautiful