During her marriage to Theodosius, she gave birth to two sons – future Emperors Arcadius and Honorius – and a daughter, Aelia Pulcheria.

[1] A passage of Themistius (Oratio XVI, De Saturnino) has been interpreted to identify Flaccilla's father as Claudius Antonius, Praetorian prefect of Gaul from 376 to 377 and Roman consul in 382.

[2] In 1967, John Robert Martindale, later one of several article writers in the Prosopography of the Later Roman Empire, suggested that the passage actually identifies Antonius as the brother-in-law of Theodosius.

His nephew and co-emperor Gratian appointed Theodosius, magister militum per Illyricum, to succeed Valens on 19 January 379.

[9] Ambrose and Gregory of Nyssa praise her Christian virtue and comment on her role as "a leader of justice" and "pillar of the Church".