After the assassination of Severus Alexander, the army elevated Maximinus Thrax, marking the start of the ‘barracks emperor’ pattern that helped drive political instability during the crisis.
A tax revolt in Africa and Senate-backed opposition to Maximinus triggered rapid imperial turnover (Gordian I & II, Pupienus, Balbinus, and Gordian III), highlighting the breakdown of orderly succession.
Following Gordian III’s death, Philip negotiated peace with the Sasanian Empire and ruled until 249, but continued military pressures and internal dissent set the stage for another overthrow.
In 249, Danubian troops proclaimed Decius emperor; he defeated Philip near Verona and took power, reflecting how frontier armies increasingly made and unmade emperors.
Decius and his son/co-emperor Herennius Etruscus were killed fighting Goths in summer 251, a major military disaster that underscored Rome’s mounting frontier threats.
After Abritus, the army elevated Trebonianus Gallus; he briefly recognized Hostilian as co-emperor, illustrating attempts to stabilize legitimacy amid repeated coups.
Valerian rose to the throne in 253 (soon associating his son Gallienus), but simultaneous wars and usurpations across regions strained central control.
In 260, the Sasanian king Shapur I defeated and captured Emperor Valerian at Edessa—the first time a reigning Roman emperor was taken prisoner—triggering further fragmentation and usurpations.
Around 260, Postumus was hailed in the western provinces, creating a breakaway regime (Gallic Empire) that controlled Gaul, parts of Germania, Britannia, and at times Hispania, formalizing the empire’s political split.
A major Roman victory near Naissus (dated 268 or 269) helped blunt large-scale Gothic incursions in the Balkans; ancient sources and modern historians treat it as a turning point in the crisis’ military phase.
In September 270, Aurelian took power after Claudius II and Quintillus, launching an aggressive program of reconquest and frontier defense that would reverse the empire’s fragmentation.
Aurelian campaigned against the Palmyrene breakaway, defeating Zenobia’s forces in 272 and bringing Palmyra back under Roman control; a further revolt in 273 was suppressed.
In 274, Aurelian defeated Tetricus I at the Battle of Châlons, ending the Gallic Empire and reunifying the Roman Empire under a single central authority.
Diocletian was acclaimed emperor in November 284 after Numerian’s death, a widely used endpoint for the Crisis of the Third Century because it initiated sustained structural stabilization of imperial rule.
Crisis of the Third Century: Usurpations, Invasions, and Breakaway States (235–284 CE)
