Fragments of the frescoes decorating the walls and the burial monuments of Bernabò and his wife have been preserved and transferred to the Sforza Castle Civic Museums (Museo d'Arte Antica).

The initial church had Paleochristian origins, dating back to the 5th century, with a single nave on a rectangular plan, 17 metres (56 feet) wide and about 35 m (115 ft) long.

The early Christian origin was confirmed by the discovery in 1949 of a tomb along the wall of the first church, with frescoes on the external surface that go back to a period between the 5th and 6th centuries.

[1] In the second half of the 12th century, the church was almost demolished during the wars of Emperor Frederick Barbarossa against Milan and subsequently rebuilt in Romanesque style.

[8] In 1384, on the death of his wife, Regina Della Scala, Bernabò had her body placed in the church inside a sarcophagus built by the workshop of Bonino da Campione.

[14] Despite the opposition of the institutions responsible for cultural heritage conservation, the municipal administration suddenly decided to demolish the front part of the church.

The Waldensian Milanese community bought the surviving portion, undertaking the recovery of the ancient façade, which was dismantled and reassembled in the new position, oblique to the previous one.

[18] The underground crypt, which survived the demolition, can be visited in Piazza Missori under the vestige of the apse[19] The façade is visible from Via Francesco Sforza in the newly built Waldesian church.

The Sforza Castle Museum houses the funerary monuments of Bernabò Visconti and his wife Regina Della Scala, the statue of Saint John the Evangelist, and frescos discovered in the church during its demolition.