According to the writings of Ennodius, bishop of Pavia in early 6th-century, Marolus was born on the banks of the Tigris in Mesopotamia. Probably due to the persecutions by Shapur II, Marolus moved before 380 to Syria where he grew up. He later moved to Rome, where he became friend of Pope Innocent I, and finally to Milan, where he became the bishop in 408.
