Milan, crossroads of travel between Italy and everything north of the Alps, hosted a recently elected pope.
The 1417 election in Constance of...More......
...Martin V, of the powerful Roman Colonna family, brought an end to the schism that had plagued Christendom.
On his way back to Rome, the pope stopped in Milan, and, in 1418, blessed the principal altar of the city's newly begun Duomo (newly begun in cathedral-building terms, that is, almost 20 years earlier).
To commemorate the event, Jacopino da Tradate was commissioned to create this image of the pope (1424).
It is visible in the Duomo's right hand part of the ambulatory...when it's open....
Not quite a "This day in Milan's history,...," but appropriate for today's historic stepping down of a reigning pope, only the second time ever in history (and perhaps the first time willingly).
One point for the first person to know (without looking it up!) who the first was, when and why...O.K., three points for all three!