Initially the operation was successful, but soon the Goths, led by general Uraias, allied with the Burgundians and besieged the town as they considered the support Milan gave to the Byzantines to be a betrayal.

In 544-545 Dacius was in Constantinople where he witnessed the promulgation by the Emperor Justinian I of an edict in which the "Three Chapters" (i.e. some writings of Theodore of Mopsuestia, Theodoret of Cyrus and Ibas of Edessa) were anathematized.

[3] Dacius' body was later translated from Chalcedon to Milan and buried in the Church of San Vittore al Corpo (Saint Victor Maurus) where it is still venerated.

In Chapter 4 (Book 3) of his Dialogues, Gregory the Great describes Dacius as an exorcist:[5] In the time of the same Emperor, Datius, Bishop of Milan, about matters of religion, travelled to Constantinople.

In the dead of the night, when the man of God was asleep, the devil began, with a huge noise and great outcry, to imitate the roaring of lions, the bleating of sheep, the braying of asses, the hissing of serpents, the grunting of hogs, and the screeching of rats.

But I will now surcease from speaking of things done in former times, and come to such miracles as have happened in our own days.To Dacius was wrongly attributed a legendary history of the first bishops of Milan up to Maternus, known as Datiana Historia Ecclesiae Mediolanensis.