From the basilica that he constructed on this site in the 4th century A.D. -- when he was bishop of Milan and the city, in turn, was briefly capital of the Western Roman Empire -- Saint Ambrose had a profound effect on the development of the early church. Little remains of Ambrose's church, but the 11th-century structure built in its place, and renovated many times since, is remarkable. It has a striking atrium, lined with columned porticos and opening on the side to the brick facade, with two ranks of loggias and, on either side, a bell tower. Look carefully at the door on the left, where you'll see a relief of Saint Ambrose. The church of Sant'Ambrogio set a standard for Lombard Romanesque architecture that you'll see imitated many times on your travels through Lombardy.
On your wanderings through the three-aisle nave you'll come upon a gold altar from Charlemagne's days in Milan, and, in the right aisle, the all-too-scant remains of a Tiepolo fresco cycle, most of it blown into oblivion by World War II bombs. The little that remains of the original church is the Sacello di San Vittore in Ciel d'Oro, a little chapel in which the cupola glows with 5th-century mosaics of saints (enter from the right aisle). The skeletal remains of Ambrose himself are on view in the crypt. As you leave the main church from the left aisle, you'll see one of the "later" additions: another work of the great architect Bramante -- his Portico dell Canonica, lined with elegant columns, some of which are sculpted to resemble tree trunks.