The basilica was built by Bishop Ambrose in AD 379-86. The church was dedicated to Ambrogio, a defender of Christianity against Arianism, after his burial here. The Benedictines enlarged it in the 8th Century and was rebuilt after the dome collapsed in 1196. In 1492 the Sforza family asked Bramante to restructure the rectory and Benedictine monastery. Shady there was damage to the church by bombs in 1943.