Aelia Flavia Flaccilla was a Roman empress and first wife of the Roman Emperor Theodosius I. She was of Hispanian Roman descent. During her marriage to Theodosius, she gave birth to two sons – future Emperors Arcadius and Honorius – and a daughter, Aelia Pulcheria.

Theodosius I, also called Theodosius the Great, was a Roman emperor from 379 to 395. During his reign, he succeeded in a crucial war against the Goths, as well as in two civil wars, and was instrumental in establishing the creed of Nicaea as the orthodox doctrine for Christianity. Theodosius was the last emperor to rule the entire Roman Empire before its administration was permanently split between the West and East.