The first part to be built was the octagonal dome, covered externally by a tambour with a loggia and arcades decorated by twelve brickwork statues by Agostino De Fondulis, designed in Lombard style by Giovanni Antonio Amadeo (1494-1498).

In 1506 a complex with a nave and two aisles was added to the original edifice, the former covered by a monumental barrel vault also by Amadeo; the presbytery received a polygonal ambulatory inspired to that in the Duomo.

The massive eclectic and Mannerist style façade was designed by Galeazzo Alessi in the late 16th century and was realized by Martino Bassi; it is decorated by numerous statues and reliefs by Stoldo Lorenzi and Annibale Fontana.

The interior houses numerous works by Milanese Renaissance and Baroque artists: Giovan Battista Crespi (il Cerano), Camillo and Giulio Cesare Procaccini, Carlo Francesco Nuvolone, Antonio Campi, Bergognone, Callisto Piazza and others.

Notable are the Baptism of Jesus by Gaudenzio Ferrari and Giovan Battista della Cerva, the Fall of St. Paul by Moretto and, on the altar of the right transept, an altarpiece by Paris Bordone.