 In the first half of the fourth century, Tortona was a suffragan of the diocese of Milan.The first bishop, according to Fedele Savio, was St. Innocentius, who in his opinion was the immediate predecessor of St. Exuperantius (381), the first of whom we have certain historical record, and who was highly praised in a sermon of Maximus of Turin (or of Ambrose of Milan).Few other names of bishops of the early period are known; but from the tenth century the list is more complete.