In 253, Roman Emperor Valerian promoted his son, Gallienus, to co-emperor. The duo shared power until Valerian’s untimely demise at Persian hands. Gallienus ruled alone from 260-268 before his own assassination. The emperor spent most of his time fighting insurrections throughout the empire. Gallienus achieved multiple military victories, reformed the military, but lost Gaul and Palmyra.
Valerian assumed the emperorship in 253 and immediately moved to guarantee peaceful succession. He asked the Senate to promote his son to co-emperor. Afterward, the pair divided the empire in two in order to meet multiple threats. Valerian moved east to battle Goths and Sassanids while Gallienus countered the barbarian threat posed by the German tribes.
Gallienus spent most of his time fighting in Germany. Around 259, a Roman governor revolted while both emperors were preoccupied. Around this time, the Persians captured Valerian, which left Gallienus alone to face Governor Ingenuus’ threat. Gallienus’ cavalry promptly defeated the upstart. Ingenuus drowned in the confusion. Meanwhile, Valerian died in Persian hands.
Valerian’s capture and death left Gallienus Rome’s sole ruler. The emperor spent the last decade of his life trying to hold the empire together and combating a number of insurrections and invasions. Gallienus defeated Germanic tribes in Gaul in 259. Then, he fought revolts in 260, 262, and 268. Gothic barbarians struck in 267. The empire was falling apart from the inside and out.
The emperor tried to reform the military to combat multiple threats. He created the first all-cavalry units in history in order to dispatch them to danger spots quickly. Diocletian later adopted the cavalry in his own set of reforms. Additionally, he refused to allow senators to serve as military commanders. This undercut their authority and limited their opportunity to foment revolt.
Despite the reforms, the empire lost Gaul and Palmyra to secession. Gaul, Britain, and Hispania formed the Gallic Empire, which was reconquered in 274. Palmyra formed their own empire in the east, which lasted until 273. Gallienus failed to reincorporate these regions into the empire during his lifetime. This left a black mark on his record that historians have held against him for nearly 2,000 years.
A cavalry commander sensed weakness and decided to challenge the emperor for the throne in 268. Gallienus defeated the mutineer and chased him to Milan. Then, the emperor’s own supporters assassinated him. He was lured out of his tent without his guards and chopped down. Immediately afterward, the Senate executed Gallienus’ family against the conspirators’ wishes. Claudius II seized the throne and died in battle two years later.
Gallienus faced the worst the Crisis of the Third Century offered. He reformed the military into a rapid strike force and undercut political generals. The emperor also put down several revolts and blunted several invasions. On the other hand, the empire split in three under his rule. However, he never had the opportunity for reunification. In the end, he met the same fate as many of his predecessors and successors.