context: At that time, the diocese of Milan, like the rest of the church, was deeply divided between Trinitarians who favor Trinity and the Aryans who opposed it. In 374, Bishop Auxentius of Milan died, and Nicea's Creedists and Areians competed for succession. The prefect personally went to the cathedral where the choice was made, to prevent a bigger riot that was difficult to avoid in that situation. According to the story, he was interrupted by the cry of "Ambrosius Bishop!", Which others joined in, and Ambrosius was unanimously elected bishop.
question: When did St. Ambrosius become Bishop of Milan?
answers.text: 374