Flavianus of Montefiascone was a 4th-century Roman patrician and martyr. According to hagiographical tradition, he served as the prefect of Rome during the reigns of Constantine II and Constantius II. He was married to Saint Daphrosa and was the father of two daughters, Viviana and Demetria, who are also recognized as saints. Following the rise of Emperor Julian, who reinstated persecutions against Christians, Flavianus lost his position to a pagan rival named Apronianus.