In olden days in Florence, many of the owners of palazzi also owned vineyards and produced wine.
Ordinary folks (that would be you and me), could take their empty bottles (or whatever they used to hold wine in those days) to the palace of their choice, and put the empty container(s) and money into the little openings designed especially for this purpose. The lord of the manor, or more likely one of the servants, would replace the empty bottle(s) with wine from their vineyard. And, leave any change owing, I hope.
You can spot many of these former wine windows as you walk around in Florence. They really are like those pissotte in Venice, once you see one, you start to spot them all over the place. So, along with towers and tabernacles, you can look forward to being introduced to these little fragments from the history of Florence.
Here’s a little sample found in about half an hour this morning, in the Oltrarno (the ‘other’ side of the Arno River).