The basement of the crypt of Basilca Sant'Ambrogio, which is supported by numerous columns, was renovated in the 1700s and lost its medieval appearance. Near the martyrs Gervasius and Protase in one of the rooms you can see the large silver and crystal urn that shows, a bit morbidly, the remains of Saint Ambrose. If you cross the crypt and exit through the left nave's side door, one last surprise awaits you.
This elegant Renaissance portico was built at the end of the 1400s by the great architect Donato Bramante (the same who designed the Holy Mary of Grace project!) on the orders of the Duke of Milan, Ludovico il Moro. You can see the duke portrayed in prayer in the bas-relief under the main arch. Carefully observe some of the stone columns, and you'll notice that they're carved as if they were recently-pruned trees!