The Valentinianic or Valentinian dynasty was a ruling house of five generations of dynasts, including five Roman emperors during Late Antiquity, lasting nearly a hundred years from the mid fourth to the mid fifth century. They succeeded the Constantinian dynasty () and reigned over the Roman Empire from 364 to 392 and from 425 to 455, with an interregnum (392–423), during which the Theodosian dynasty ruled and eventually succeeded them. The Theodosians, who intermarried into the Valentinian house, ruled concurrently in the east after 379.
The Valentinian dynasty's patriarch was Gratianus Funarius, whose sons Valentinian I and Valens were both made Roman emperors in 364. Valentinian I's two sons, Gratian and Valentinian II both became emperors. Valentinian I's daughter Galla married Theodosius the Great, the emperor of the eastern empire, who with his descendants formed the Theodosian dynasty (). In turn, their daughter, Galla Placidia married a later emperor, Constantius III (). Their son, Valentinian III (), who ruled in the west, was the last emperor of the dynasty, whose death marked the end of dynasties in the western empire. During the interregnum, Theodosius' son Honorius ruled in the west, and concurrently with Galla Placidia from 421. The dynasty has been labelled as Pannonian, based on the family origin in Pannonia Secunda in the western Balkans.
Under the Valentinians, dynastic rule was consolidated and the division of the empire into west and east became increasingly entrenched. The empire was subject to repeated incursions along its borders, with the Danube frontier eventually collapsing in the northeast and barbarian invasions in the west eventually reaching Italy, and culminating with the sack of Rome in 410, which foreshadowed the eventual dissolution of the western empire in the late fifth century.
Background
The Valentinian dynasty (364–455) was a ruling house during the Late Roman Empire (284–476), in Late antiquity (adj.late antique), including the turbulent years of the late fourth century, and the last dynasty of the western empire. The death of Julian () was a pivotal point in the history of the empire. The thirty years from the death of Julian, which ended the Constantinian dynasty, to the death of Valentinian II () ending the first Valentinian dynasty, were one of the most critical periods in the late Roman empire, structuring the empire in ways that would have long lasting consequences. The succeeding thirty years (395–425) from the death of Theodosius I to the death of his sons and ascent of Valentinian III () saw the foundations of the Byzantine empire in the east and the replacement of the western Roman empire with European kingdoms together with a series of events that led to the emergence of the mediaeval Islamic states. The period of the preceding Constantinian age (293–363) reaffirmed the importance of dynasty in legitimacy and succession. This new dynastic structure would last until 454. The house of Valentinian (the Valentiniani) established continuity and succession from the Constantinians through marriages to a granddaughter and grand-niece of Constantine. This granddaughter, Constantia (362–383), the only surviving child of Constantius II (), played an important role as a symbol of her dynasty for decades. The Constantinian legacy being described as the "indelible glow of empire". While imperial heirs were relatively rare in this period, the marriages of imperial women raised special concerns, as possibly leading to the raising of pretenders to the throne. A number of them, such as Gratian's half-sisters, took a vow to become dedicated virgins (). Yet it was also an era in which women, either as empresses or as emperor consorts, rose to unprecedented power. Another feature of this dynasty was the successive appointment of child emperors, radically changing the traditional image of emperors as men of deeds. With Valentinian's division of the empire () in a new way, in 364, the two parts of the empire (), east and west would progressively develop their own histories, until the split became permanent on the death of Theodosius I ().