The walls of this chapel are decorated with hundreds of human skulls and bones of unknown origin. The assumption is that they came from a hospital that was located near the church and that some of them may have belonged to the criminals who were sentenced to death.
Myths, legends, and conspiracy theories connect these bones to the illegitimate children of young women from local noble families. Another theory links them to tortured Christian martyrs who were executed.
The basilica itself is built in the form of an octagon. It was built in the 12th century, at around 1145 AD, and was restored over the years. The main renovation was done in the 17th century.
It is characterized by decorations from different periods, from Baroque decorations to Rococo motifs. The niches and the doors of the basilica, for example, are decorated with Rococo style, and in them, the motif of skulls and bones is also incorporated.
The church contains a variety of frescoes made over the centuries. These are frescoes that were painted here during the period between the 16th and the 18th centuries. These frescoes usually describe various saints whose stories appear in the New Testament. One of them also includes St. Ambrose, the patron of the city of Milan and who served as the bishop of Milan. Saint Ambrose is also known here as one who did not shrink from the fear of the Roman emperors and succeeded in establishing the church's control over their secular rule and the Roman Empire.