1,5 km south-west of the castle’s main entrance, or just a 10 minutes walk away from Santa Maria delle Grazie, there is another church, dedicated to the saint considered as guardian of the city and regarded as the second most important church after the cathedral.

This Basilica is the oldest church in Milan: it was built between 379 and 386 by Ambrogio (Ambrose in English), bishop of Milan, in the place where martyrs of the early Christianity were executed and buried by the Romans. The church was then dedicated to them and filled with memorabilia of these people; eventually Ambrogio himself was buried inside and the church changed its name after him.