Valentinian III in the context of "Theodosian dynasty"

The pontifex maximus (Latin for 'supreme pontiff') was the chief high priest of the College of Pontiffs (Collegium Pontificum) in ancient Rome. This was the most important position in the ancient Roman religion, open only to patricians until 254 BC, when a plebeian first held this position. Although in fact the most powerful office in the Roman priesthood, the pontifex maximus was officially ranked fifth in the ranking of the highest Roman priests (Ordo Sacerdotum), behind the Rex Sacrorum and the flamines maiores (Flamen Dialis, Flamen Martialis, Flamen Quirinalis).

A distinctly religious office under the early Roman Republic, it gradually became politicized until, beginning with Augustus, it was subsumed into the position of emperor in the Roman imperial period. Subsequent emperors were styled pontifex maximus well into Late Antiquity, including Gratian (r. 367–383), but during Gratian's reign the phrase was replaced in imperial titulature with the Latin phrase: pontifex inclytus ("honourable pontiff"), an example followed by Gratian's junior co-emperor Theodosius the Great and which was used by emperors thereafter including the co-augusti Valentinian III (r. 425–455), Marcian (r. 450–457) and the augustus Anastasius Dicorus (r. 491–518). The first to adopt the inclytus alternative to maximus may have been the rebel augustus Magnus Maximus (r. 383–388).

The Valentinian dynasty, commonly known as the Valentinianic 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 (r. 306–363) and reigned over the Roman Empire from 364 to 392 and from 425 to 455, with an interregnum (392–425), 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 (r. 379–457). In turn, their daughter, Galla Placidia married a later emperor, Constantius III (r. 421–421). Their son, Valentinian III (r. 425–455), 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 Constantius III in 421. The dynasty has been labelled as Pannonian, based on the family origin in Pannonia Secunda in the western Balkans.

The Codex Theodosianus ("Theodosian Code") is a compilation of the laws of the Roman Empire made by the Christian emperors from 311 A.D. until 437 A.D. A commission was established by Emperor Theodosius II and his co-emperor Valentinian III on 26 March 429 and the compilation was published by a constitution of 15 February 438. It went into force in the eastern and western parts of the empire on 1 January 439. About one-quarter of the original text of the codex is also found in the Breviary of Alaric (also called Lex Romana Visigothorum), promulgated on 2 February 506 by Visigoth King Alaric II.

The sack of Rome in 455 was carried out by the Vandals led by their king Gaiseric.

A 442 treaty between the Western Roman Empire and Vandal Kingdom included a marriage of state between the daughter of Roman Emperor Valentinian III and the son of Gaiseric. Valentinian's successor Petronius Maximus violated the treaty by marrying his son to Valentinian's daughter, and Gaiseric retaliated with an invasion of Italy. Maximus did not organise a defence of Rome and was lynched by a Roman mob while trying to escape the city. Pope Leo I convinced Gaiseric to avoid the use of violence against residents of the city. The Vandals looted Rome for two weeks, causing widespread destruction to the city, stripping it of most of its valuables, and taking some residents as slaves. Maximus' successor Avitus had little support which led to the outbreak of the Roman civil war of 456.

Gaiseric (c. 389 – 25 January 477), also known as Geiseric or Genseric (Latin: Gaisericus, Geisericus; reconstructed Vandalic: *Gaisarīx) was king of the Vandals and Alans from 428 to 477. He ruled over a kingdom and played a key role in the decline of the Western Roman Empire during the 5th century.

The murder of Roman Emperor Valentinian III, who had betrothed his daughter to Gaiseric's son Huneric, led the Vandal king to invade Italy. The invasion culminated in his most famous exploit, the capture and plundering of Rome in June 455. Gaiseric repulsed two major attempts by both halves of the Roman Empire to reclaim North Africa, inflicting devastating defeats on the forces of Majorian in 460 and Basiliscus in 468. As a result, the Romans abandoned their campaign against the Vandals and concluded peace with Gaiseric. Gaiseric died in Carthage in 477 and was succeeded by his son, Huneric. Through his nearly fifty years of rule, Gaiseric raised a relatively inconsequential Germanic tribe to the status of a major Mediterranean power.

Flavius Aetius (also spelled Aëtius; Latin: [aːˈɛtiʊs]; c. 390 – 21 September 454) was a Roman general and statesman of the closing period of the Western Roman Empire. He was a military commander and the most influential man in the Empire for two decades (433–454). He managed policy in regard to the attacks of barbarian federates settled throughout the West. Notably, he mustered a large Roman and allied (foederati) army in the Battle of the Catalaunian Plains, ending an invasion of Gaul by Attila in 451, though the Hun and his subjugated allies still managed to invade Italy the following year, an incursion best remembered for the Sack of Aquileia and the intercession of Pope Leo I. In 454, he was assassinated by the emperor Valentinian III.

Aetius has often been called the "Last of the Romans". Edward Gibbon refers to him as "the man universally celebrated as the terror of Barbarians and the support of the Republic" for his victory at the Catalaunian Plains. J.B. Bury notes, "That he was the one prop and stay of the Western Empire during his life time was the unanimous verdict of his contemporaries."

Galla Placidia (392/93 – 27 November 450), daughter of the Roman emperor Theodosius I, was a mother, tutor, and advisor to emperor Valentinian III. She was queen consort to Ataulf, King of the Visigoths from 414 until his death in 415, briefly empress consort to Constantius III in 421, and managed the government administration as a regent during the early reign of Valentinian III until her death.

The terms minority reign and royal minority refer to the period of a sovereign's rule when he or she is legally a minor. Minority reigns are of their nature times when politicians and advisors can be especially competitive. Some scholars claim that, in Britain, primogeniture, the growth of conciliar government, and the emergence of the Parliament as a representative and administrative force all occurred within the context of the minority reigns.

Minority reigns also characterized a period in the Roman Empire from 367 to 455, the years that preceded the reign of Valentinian III, who also became emperor at the age of six. The succession of child-turned-adult emperors led to the so-called infantilization of the imperial office, which had taken hold during the long reign of Honorius, Valentinian's predecessor. Here, the imperial office operated within a severely curtailed system compared to its authority a century prior.