According to the tradition, Eustorgius was a noble Greek. He was the legate of Milan and he was elected as bishop at the death of Protasius in 343. Eustorgius traveled to Constantinople to have his election as bishop confirmed by the Emperor, and in that occasion Emperor donated to him the relics of the Three Magi which he translated from Constantinople to Milan.
From 345 to 346 and from 347 to 348, he held two synods. He also began construction of churches and basilicas in Milan. Saint Athanasius called him a "defender of the faith" and mentions him as an opponent of Arianism. Saint Ambrose called him by the honorable title of "confessor", and just in such a way some verses concerning Milan in ca. 700. His name was included in the Ambrosian Rite  and his cult in Milan is testified by the presence of five churches dedicated to him (as testified in a 14th-century document, Liber notitiae sanctorum Mediolani ), the best known of which is the Basilica of Sant'Eustorgio. A 5th or 6th century song indicates that he was a famous holy man and that he had built a great sarcophagus. And two little cows had transported the large shrine. Eustorgius was perhaps buried in the cemetery on the grounds of Sant'Eustorgio, which was located outside the Roman walls along the road to