Built by Bishop Ambrose between the 379 and the 386, the Basilica Martyrum was dedicated after that was buried there. It was enlarged from the VIII century by the Benedictine monks. In the IX century the Archbishop Ansperto erected the atrium, rebuilt in the 12th and in the XI began the reconstruction of the Church. In 1196, the collapse of the dome imposed the reconstruction of the times and of the pulpit. In 1492, Bramante was commissioned by the Sforza family of restructuring of the rectory for religious joints in the XII century and the benedictine monastery where they had just settled the Cistercians. Escaped to a new repair in the XVII century, it was seriously damaged by bombing in 1943.