This Diocese of Millain contained Liguria with Insubria, the Alpes Cottiae and Rhaetia; and was divided from the Diocese of Aquileia by the river Addua. In the year 844, the Bishop of Millain broke off from the See of Rome, and continued in this separation about 200 years, as is thus related by Sigonius: Eodem anno Angilbertus Mediolanensis Archiepiscopus ab Ecclesia Romana parum comperta de causa descivit, tantumque exemplo in posterum valuit, ut non nisi post ducentos annos Ecclesia Mediolanensis ad Romanae obedientiam auctoritatemque redierit.
The Bishop of Ravenna, the Metropolis of Flaminia and Aemilia, was also subject to the Pope: for Zosimus, A.C. 417, excommunicated some of the Presbyters of that Church, and wrote a comminatory Epistle about them to the Clergy of that Church as a branch of the Roman Church: In sua, saith he, hoc est, in Ecclesia nostra Romana. When those of Ravenna, having elected a new Bishop, gave notice thereof to Pope Sixtus, the Pope set him aside, and ordained Peter Chrysologus in his room. Chrysologus in his Epistle to Eutyches, extant in the Acts of the Council of Chalcedon, wrote thus: Nos pro studio pacis & fidei, extra consensum Romanae civitatis Episcopi, causas fidei audire non possimus. Pope Leo I. being consulted by Leo Bishop of Ravenna about some questions, answered him by a decretal Epistle A.C. 451. And Pope Gregory the great, reprehending John Bishop of Ravenna about the use of the Pallium, tells him of a Precept of one of his Predecessors, Pope John, commanding that all the Privileges formerly granted to the Bishop and Church of Ravenna should be kept: to this John returned a submissive answer; and after his death Pope Gregory ordered a visitation of the Church of Ravenna, confirmed the privileges heretofore granted them, and sent his Pallium, as of ancient custom, to their new Bishop Marinian. Yet this Church revolted sometimes from the Church of Rome, but returned again to its obedience.