The construction was begun by Gian Giacomo Dolcebuono and Giovanni Battagio in 1493, to house a miraculous icon of the Madonna, initially on the central plan. 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 to the original edifice a complex with nave and two aisles was added, the former covered by a monumental barrel vault also by Amadeo; the presbytery received a polygonal ambulatoryinspired to that in the Duomo.