'Pax Romana' Undone: The Crisis of the Third Century Begins, 235-244AD
From the ascension of Augustus as emperor in 27BCE to the death of Marcus Aurelius in 180AD, the Roman Empire experienced what historians have termed the 'Pax Romana' (Roman Peace); a 200-year period of relative peace and minimal territorial expansion. Cut to 60 years later, and the Empire was in the beginning of a 50 year civil conflict, characterised by numerous imperial claimants fighting one another for control, runaway economic inflation, and military threats on the Empire's borders. The 'Crisis of the Third Century' nearly destroyed one of the largest empires that had ever existed, and is an important period in the changes to the institutions and nature of the Roman Empire.
Maximinus Thrax, First Emperor of the Crisis: 235AD
The Severan Dynasty of emperors had ruled the Roman Empire since 193AD, and their last emperor, Severus Alexander, was assassinated by his own soldiers in 235AD out of frustration with his diplomatic dealings towards the Germanic tribes. One of his subordinates, a Thracian called Maximinus Thrax, was elevated to emperor by the troops. A physically hulking, stern and ruthless commander, Maximinus was seen by the soldiery as one of their own, someone who would bring them glory in combat, and were pleased when he quickly set about launching a campaign against the Germanic Alemanni tribe. Maximinus further set up a position at Sirmium in modern-day Serbia in order to keep a watchful eye on some other barbarian tribes, the Dacians and Sarmatians.
Maximinus' campaigns were deeply expensive. He went further by upping the pay of the military, and in order to pay for this and the campaign he instituted a draconian and highly unpopular taxation policy. He didn't spend any time explaining nor justifying this tax increase and never bothered travelling to Rome to enforce his rule, which helped spread rumours and accusations of corruption against him. Further, the military by this point had a heavy number of former barbarian soldiers, including Maximinus' himself, which led many Romans to see the army as a 'foreign', unruly force of barbarians not deserving of their taxes, strengthening discontent towards his rule.
The Gordians, The Senate, and the End of Maximinus: 238AD
The frustration with Maximinus' rule came to a head in 238AD when a group of landowners in Thysdrus, modern-day Tunisia, decided to murder a procurator loyal to Maximinus, and then turned to Marcus Atonius Gordianus, the aging proconsul of the region, and proclaimed his as Emperor Gordian I. Gordian I began his rival imperial reign by naming his son as his co-emperor, Gordian II.
The Roman Senate had disliked Maximinus right from the start due to his barbarian origins, regardless of the fact that the Emperor Caracalla's edict in 212AD had granted Roman citizenship to all freeborn inhabitants of the Empire. They nevertheless passed the legislation required to give Maximinus imperial powers. When the Gordians came into the picture, the Senate took the opportunity to proscribe Maximinus as an enemy of the state and confirmed the Gordians as the rightful co-emperors. Gordian I and II undertook a three-week long insurgency against Maximinus, but was ended quickly after the Numidian governer Capelianus, who was loyal to Maximinus, managed to turn the Gordian's forces against them, and their deaths ended their revolt.
The deaths of the two Gordians put the Senate in an uncomfortable position. They could either admit error to Maximinus and accept his rule, or they could search for another rival claiming to lend their backing to. They decided to elect for the latter option, and appointed two of their own senators, Pupienus and Balbinus, as co-emperors. Unfortunately for the Senate however, these two men were not widely popular. The Praetorians and the Plebs, among other groups, agitated for the young nephew of Gordian II to be the new emperor. Pupienus and Balbinus relented and named Gordian III as successor.
The Senate's decision led Maximinus Thrax to march on Rome to enforce his rule. However, his journey was met with harsh resistance by Pupienus who had travelled north to stop him, and he was faced with internal difficulties as low supplies led to low morale and discontent among his own men. Maximinus died at this time, and while the circumstances of his death are not known for sure, sources suggest he either killed himself after witnessing the murder of his own son, or that both he and his son were killed by his own soldiers.
Regardless, with Maximinus dead, Pupienus and Balbinus soon turned on one another, accusing each other of various conspiratorial actions. The Praetorians took their quarrelling as an opportunity to murder both of them, lifting Gordian III as the sole occupier of the imperial throne.
The Youngest Emperor, Gordian III: 238AD - 244AD
Reliable information on Gordian III's reign is scant and marred by fantasy, but some details can be concluded. Gordian III was 13, the youngest person throughout the Empire's existence to be sole emperor, and came to the throne with a fair amount of support across various groups. The Senate approved of his elevation, and he was brought to the throne by the military, who approved because, as a young man, he was under the guidance of the Timesitheus, the Praetorian Prefect, one of the highest offices in the Empire.
Despite coming into power with a lot of support, his reign did face significant challenges. Pupienus and Balbinus had been preparing to engage the Capri and Goth barbarian tribes, and their deaths left it to Gordian and Timesitheus to undertake. Timesitheus successfully managed to drive back the tribes in 238 and again in 242, but the turmoil in the Empire was exploited by the Persians, who took the opportunity to attack Mesopotamia and Syria. Gordian and Timesitheus took to the Persian front where, after some initial victories, Timesitheus died, likely of illness. He was replaced as Praetorian Prefect by Marcus Julius Philippus, commonly known to history as Philip the Arab.
The last couple of years of Gordian III's reign are obscure. The young emperor died in 244, with some sources suggesting he died in battle against the Persians, and others suggesting he was murder by disaffected ranks in his own army, possibly under the direction of Philip. Nevertheless, the young emperor died, and Philip the Arab was elevated to the emperorship in his place. The first stage of the Third Century Crisis had ended.
Pat Southern, The Roman Empire from Severus to Constantine
David S. Potter, The Roman Empire at Bay, AD180-394
Edward Gibbon, The History of the Decline and Fall of the Roman Empire (Much of this work's interpretations are no longer accepted but still a good introduction to Roman history)