Introduction to the main entrance of the church: The six huge stone pillars on the front of the cathedral are separated by five bronze doors. The lower half of the door frame is Baroque and the upper half is Gothic. The door is made of bronze and weighs about 7.5 tons. It is covered with reliefs.
The first bronze door on the left was completed in 1948 and represents the decree of Emperor Constantine; the second bronze door was made in 1950 and tells the life of San Ambrogio. The three largest bronze doors were completed in 1906, weighing 37 tons, and depict the life of the Virgin Mary; the fourth bronze door was completed in 1950, telling the story from the death of German Emperor Frederick II to Leni The history of Milan during the Battle of Arno; the fifth bronze door, completed in 1965, shows the history of the cathedral from the time of San Carlo Borromeo.