Marcellina was born into a Roman Christian household in Trier, Gaul, in the year 330. Her father held the position of Praetorian Prefect of Gaul. She was Ambrose of Milan's sister, and she was older than her two brothers. She appears to have taken care for her younger brothers, Ambrose and Satyrus, when their parents died. When they were grown up, she married a wealthy citizen of Milan named Marcianus and moved with him to his home town. There she devoted herself to helping orphans and poor people. One day a nobleman named Tarquinius came to visit her in Milan. He was amazed by her kindness and told her that he would like her to go live with him in his castle near Rome. But Marcellina answered that she could not leave Milan because there were still many people who needed her help. Then Tarquinius promised that if she went with him he would never send her away from anyone who needed her assistance. Finally, Marcellina agreed to go with Tarquinius but only if her brothers would also go with her. So all four of them went to live at the castle of Tarquinia (near Rome). It is said that they were very happy there! One night after they had gone to bed, there appeared to them an angel who told them that they should return to Milan as soon as possible because a terrible plague was going to break out in Rome and kill many people. When they got back to Milan, they found that many citizens had died of the plague.