A barracks emperor (also called a "soldier emperor") was a Roman emperor who seized power by virtue of his command of the army. Barracks emperors were especially common from 235 to 284 AD, during the Crisis of the Third Century, which began with the assassination of Severus Alexander. Beginning with Maximinus Thrax, there were approximately fourteen barracks emperors in 33 years, which produced an average reign of a little over two years apiece. The resulting instability in the imperial office and the nearly-constant state of civil war and insurrection threatened to destroy the Roman Empire from within and left it vulnerable to attack from external adversaries.
The barracks emperors tended to be low-class commoners, often from outlying parts of the empire. The first barracks emperor, Maximinus Thrax, had begun his military career as an enlisted soldier. A barracks emperor could not boast of a distinguished family name or a successful career as a statesman or public servant. Rather, he had only his military career to recommend himself, and his only influence had been though the soldiers loyal to his command.
Some of the soldier emperors were members of the equestrian class who had worked their way up to a sufficient position of influence within their legion that the soldiers would support a bid for power, but that was a risky undertaking because those soldiers could withdraw their support at any time and perhaps shift it to another military leader who looked more promising at the time.
Because the barracks emperors were frequently border commanders, the act of overthrowing the reigning emperor and seizing power for themselves left large gaps in the empire's border defences that could be exploited by Rome's enemies. That led to the Germanic incursion into Roman territory in the 260s and resulted in the construction of the Aurelian Walls around Rome. The barracks emperors also used state money to pay their troops since no emperor who had come into power by force of arms could afford to allow his soldiers to become disaffected, and public works and infrastructure fell into ruin. To accommodate the vast demands of buying off their soldiers, the state often simply seized private property, which damaged the economy and drove up inflation.
In 284, a barracks emperor, Diocletian, a cavalry commander, seized power. Diocletian instituted a number of reforms designed to stabilize the empire and the imperial office, brought an end to the Crisis of the Third Century and inaugurated the Dominate era of Roman history.
Although further emperors would don the purple on the basis of military power (such as Constantine I, Valentinian I, and Theodosius I) the phenomenon of the barracks emperors died out, to be replaced in the late imperial era by shadow emperors like Stilicho, Constantius III, Flavius Aëtius, Avitus, Ricimer, Gundobad, Flavius Orestes and Odoacer. They were military strongmen who effectually ruled the empire as imperial generalissimos controlling weak-willed puppet emperors, rather than taking the title themselves.
| Reign | Incumbent | Notes | |
|---|---|---|---|
| February/March 235 to March/April 238 | Maximinus Thrax | Murdered by his own troops | |
| early 238 | Gordian I | Governor in Africa, declared co-emperor with his son Gordian II by popular demand. Committed suicide after defeat in battle against the governor of Numidia | |
| early January/March 238 to late January/April 238 | Gordian II | Son of and co-emperor with Gordian I. Killed in battle against the governor of Numidia | |
| April to July 238 | Pupienus and Balbinus | Senators elected as co-emperors by Roman Senate upon the failure of the African rebellion. Murdered by the Praetorians | |
| May 238 to February 244 | Gordian III | Grandson of Gordian I – elected by Senate at 13. Either killed in battle against Persians under Shapur I in modern-day Iraq (Roman histories do not mention the battle) or murdered by the Praetorian Prefect Philip, who succeeded him as Philip the Arab | |
| 240 to 240 | Sabinianus | Proclaimed himself emperor; defeated in battle and surrendered to the imperial authorities by his own supporters | |
| February 244 to September/October 249 | Philip the Arab | Killed in battle by Decius near modern-day Verona | |
| 248 to 248 | Pacatianus | Proclaimed himself emperor; murdered by his own soldiers | |
| 248 to 248 | Jotapian | Claimant; murdered by his own soldiers | |
| 248 to 248 | Silbannacus | Usurper, likely held brief control of the mint in Rome | |
| 249 to June 251 | Decius | Appointed by Philip the Arab to defeat Pacantius. Proclaimed emperor by the Danubian armies. Killed in battle against the Goths | |
| 249 to 252 | Priscus | Proclaimed himself emperor in the Eastern provinces with Gothic support | |
| 250 to 250 | Licinianus | Claimant | |
| early 251 to 1 July 251 | Herennius Etruscus | Co-emperor with his father Decius. Killed in battle against Goths | |
| 251 to 251 | Hostilian | Younger brother of Herennius Etruscus, whom he succeeded as emperor. His authority did not extend far beyond Rome, where he soon died in an outbreak of plague | |
| June 251 to August 253 | Gallus | Proclaimed emperor by the army after the deaths of Decius and Herennius Etruscus. Co-ruled with his son Volusianus. Murdered by his own soldiers | |
| July 251 to August 253 | Volusianus | Co-emperor with his father Trebonianus Gallus. Murdered by his own soldiers | |
| August 253 to October 253 | Aemilian | Governor of Moesia Superior and Pannonia who defeated a Gothic army and was proclaimed emperor by his soldiers. Murdered by his own soldiers when they saw that they could not defeat the army of Valerian, who came to avenge Trebonianus Gallus | |
| 253 to June 260 | Valerian | Governor of the Rhine provinces. Co-emperor with Gallienus; captured by Persians: died in captivity | |
| 253 to September 268 | Gallienus | Co-emperor with Valerian 253 to 260, sole emperor from 260 to 268; murdered | |
| 258 or June 260 | Ingenuus | Proclaimed himself emperor | |
| 260 | Regalianus | Proclaimed emperor | |
| 260 to 261 | Macrianus Major | Proclaimed emperor; lost and killed in battle | |
| 260 to 261 | Quietus | Claimant | |
| 261 to 261 or 262 | Mussius Aemilianus | Proclaimed emperor | |
| 268 to 268 | Aureolus | Proclaimed himself emperor; surrendered to Claudius II Gothicus |