As I said before, the Cathedral's façade is the result of centuries of work.
While the church was reaching its final size at the end the 1500s, the ancient façade of the former church Santa Maria Maggiore still stood, and was demolished gradually.
It was Cardinal Federico Borromeo, successor and cousin of Saint Charles, who decided to create an innovative and spectacular façade.
After evaluating a large number of proposals, it was decided to give the Cathedral five portals, one for each nave. The doors' decoration was entrusted to Cerano, one of the great Milanese artists of the time. Cerano wanted to tell the "stories" of five major female characters of the Bible. Why only women? you may wonder. Simple, in honor of the Virgin Mary, to whom the cathedral is dedicated, as can be seen in the writing "To nascent Mary" which stands out in Latin in the middle of the façade. The stories are told through bas-reliefs known as "formelle", or panels, which are both above and below the portals, and feature Eve (center), Esther, Jael, Judith and the Queen of Sheba.
After the portals' decoration had been finished, work on the Cathedral was interrupted again at the height of the central window.
It was only two centuries later that Napoleon Bonaparte, annoyed by the contrast between the still rough façade and the glittering mass of the Cathedral marble, ordered the façade completed. It was said and done, and the statues representing the Church and the Synagogue at the middle of the balcony were built.
The façade was only completed at the end of the 1800s, and the five bronze doors were completed even later! The first was the great central door, which dates back to 1906. If you look carefully, you'll notice that it's ruined in some places because of bombings in World War II.
FUN FACT: look carefully at the left statue on the balcony above the central door: as I said, the Church is represented by a female figure. Does something about her seem familiar? You're absolutely right, the statue's model was taken from the French sculptor Bartholdi, who designed the Statue of Liberty for the city of New York.