Theodosian dynasty

• 1. Introduction

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  The Theodosian dynasty produced five Roman emperors across a span of less than eighty years, ruling an empire that stretched from Britain to the borders of Persia. That run began on the 19th of January 379, when a Spanish general's son named Theodosius was raised to augustus at Sirmium. It ended in 457, when the last figure carrying a meaningful blood tie to that family left the throne of the East. What made this dynasty unusual was how it held together: not through any single commanding line of succession, but through marriages, regencies, and the extraordinary political careers of women who kept the imperial name alive long after the men had died. Who was the general whose execution by his own emperor set the whole saga in motion? How did a dynasty that lost control of Rome itself manage to outlast nearly everything around it?

• 2. The Elder and the Foundation

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  Flavius Theodosius, known as Count Theodosius, was a general of Hispanic origin who made his name saving Roman Britain from what the sources call the Great Conspiracy, a coordinated assault on the province that was defeated between 368 and 369. He held the rank of magister equitum, the master of cavalry, from 369 until 375, campaigning against the Alamanni in 370 and against Sarmatians in 372 or 373. His estates in the Iberian Peninsula were large enough that the future usurper Magnus Maximus was born there and claimed kinship with the family, though the sources cast doubt on that claim.

  Theodosius the Elder fell from power and was executed in 375. His son, who had been serving as military governor of Moesia Prima, retired to the Iberian Peninsula after his father's death. There he married Aelia Flaccilla in 376, and their son Arcadius was born around 377. Theodosius had returned to the Danube frontier by 378, when he was again appointed magister equitum. The death of the Emperor Valens at the hands of the Goths that same year created the opening that would transform the family's fortunes entirely. Valens left no obvious successor, and the senior augustus Gratian turned to the Spanish general's rehabilitated son to fill the gap.

• 3. Theodosius and the Church

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  On the 27th of February 380, Theodosius issued the Edict of Thessalonica, making Nicene Christianity the state religion of the Roman Empire. That decree was only the beginning. On the 10th of January 381 he issued a ruling against Christians deemed heretics; on the 8th of May he issued an edict against Manichaeism; and in mid-May he convened the First Council of Constantinople, the second ecumenical council in the Church's history, which ran until the 9th of July. On the 24th of February 391, attendance at pagan sacrifice and at pagan temples was prohibited by law, and on the 16th of June the prohibition on pagan worship was extended further.

  The relationship between Theodosius and Ambrose, bishop of Mediolanum, showed that imperial power had limits the Church was willing to contest. In spring 390, possibly in April, Theodosius's army carried out the Massacre of Thessalonica. Ambrose demanded that the emperor perform public penance. According to the 5th-century church historian Theodoret, Theodosius did exactly that: on the 25th of December 390, Christmas Day, Ambrose received him back into the Church. The Serapeum of Alexandria was destroyed in early summer 391, and by the 8th of November 392 all cult worship of the gods was forbidden by imperial law. The transformation of Roman religious life during Theodosius's reign was thorough and deliberate.

• 4. War, Usurpers, and a Unified Empire

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  Magnus Maximus was acclaimed augustus in Britain in early 383, and Theodosius initially chose diplomacy over confrontation. In summer 384, Theodosius met his co-augustus Valentinian II in northern Italy and brokered a peace between Valentinian and Maximus that held for several years. That peace broke down in 387, when Valentinian was driven from the west and reached Thessalonica, appealing to Theodosius for military support. Theodosius married Valentinian's sister Galla at Thessalonica in late autumn of that year.

  The campaign that followed was decisive. Around July 388, Magnus Maximus was defeated at Siscia and at Poetovio, and on the 28th of August he was executed by Theodosius. Damnatio memoriae was pronounced against him and his young son Flavius Victor, who was killed in Gaul by Arbogast in August or September of the same year. All inscriptions naming them were erased. Arbogast, the magister militum left to protect Valentinian, then became himself a problem: Valentinian II died on the 15th of May 392 at Vienna in Gaul, either by suicide or through Arbogast's scheming. Arbogast installed a civilian official named Eugenius as augustus at Lyon on the 22nd of August. Theodosius defeated Eugenius at the Battle of the Frigidus on the 6th of September 394. Arbogast killed himself on the 8th of September. For the first time since 364, a single man ruled the whole Roman Empire. Theodosius died in Mediolanum on the 17th of January 395, less than four months after that victory.

• 5. Galla Placidia's Pivotal Role

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  Galla Placidia was born in 392 or 393, the daughter of Theodosius's second wife Galla and therefore a daughter of the house of Valentinian as well as the house of Theodosius. After her father died and her brothers took the East and West respectively, she became a figure around whom western succession would revolve for decades. She married Athaulf, the King of the Visigoths, in 414. When he died she married the patrician Constantius in 417. Constantius was raised to augustus by Honorius in 421; he died the same year, and Galla Placidia was made augusta before being forced to flee to Constantinople.

  When Honorius died in 423 without an heir, an official named Joannes seized the western throne. Theodosius II moved to displace him, appointing Galla Placidia's young son Valentinian as caesar on the 23rd of October 424. After Joannes fell, Valentinian III was made augustus on the first anniversary of that appointment, and Galla Placidia served as regent through his youth. She died on the 25th of November 450. Her son Valentinian III ruled the western provinces until his death on the 16th of March 455. The dynasty's hold on the West ran directly through her.

• 6. The Dynasty's Long Twilight

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  Theodosius II, son of Arcadius, was the last dynastic emperor in the East by direct descent. After his death his older sister Pulcheria married the general Marcian, bringing the dynasty formally to a close in the East while technically continuing it through marriage. In the West, Petronius Maximus gained the throne by marrying Licinia Eudoxia, the daughter of Theodosius II, after Valentinian III was killed in 455. Olybrius held the western throne by virtue of his marriage to Placidia, the daughter of Valentinian III. Anthemius is sometimes counted to the dynasty because he became a son-in-law of Marcian.

  The family tree kept branching long after the dynasty's formal end in 457. Valentinian III's daughter Eudocia married Huneric, king of the Vandals, and their son Hilderic became king of the Vandals in North Africa. Placidia, another daughter of Valentinian III, married Olybrius, and their descendant line extended several more generations, with Anicia Juliana among the notable later figures. Descendants of the dynasty were still present in the East Roman nobility at Constantinople as late as the end of the 6th century, nearly two hundred years after Theodosius was first acclaimed at Sirmium. Justa Grata Honoria, the sister of Valentinian III and a granddaughter of Theodosius, was granted the title augusta and reportedly proposed marriage to Attila the Hun, though that treaty was never concluded.