Emperor A.D 253 - 268
Gallienus was made co-emperor by his father Valerian I soon after he became emperor in A. D. 253. Both Gallienus and Valerian spent most of their reigns fighting Rome's enemies in Persia, Gaul, Egypt, Syria, and along the Danube. It was a time of great political and economic upheaval called the crisis of the Third Century from which the Roman Empire almost never recovered. The rebellion of Postumus and attacks by Shapur I of Persia occupied most of Gallienus' energy. In addition, the empire went bankrupt and started issuing coins with little or no silver content, bringing about the great economic collapse of the mid Third Century.
One of the things Gallienus is remembered for is his reorganization of the army. He made mounted cavalry units a major part of the army, creating a fast, mobile strike force that could be sent to any place in the empire where trouble flared up. This force was mainly composed of cavalry, which were being used by the barbarians against Rome to great effect. Up until this time the Roman army had relied on the foot soldiers in the infantry legions. He based his new cavalry units at Ticinium in Italy. This concept was later perfected as the mobile field army of Diocletian and Constantine.
The history of this period is an alphabet soup of names of little known generals and exotic, far-off places. The one thing these odd names had in common is that they all spelled trouble for Gallienus! In 259 Postumus, the legate to the Rhine armies revolted and set up a rebel empire in Gaul, Spain, and Britain. He successfully defended it for almost ten years despite Gallienus' very vigorous attempts to crush him. Macrianus and Quietus, two sons of Valerian's quartermaster in the East, rebelled in 260 but had both been defeated and killed by 261. Odenathus governed Palmyra, supposedly in Gallienus' name but in reality he functioned as an independent king. Finally, Aureolus, commander of the new cavalry force that Gallienus had so successfully used to put down most of the rebellions and deal with the Goths, rebelled in Milan during the summer of 268. Though Aureolus was defeated, it was little benefit to Gallienus, who had only recently been murdered by his own officers. Many historians blame Gallienus for his failures, especially the economic depression and collapse of the silver coinage, but Gallienus had more problems to deal with than any one emperor could reasonably be expected to handle. He was an energetic emperor and an excellent general who probably did the best job possible under the circumstances.
In spite of his popularity with the army on account of his many victories, Gallienus was murdered by his senior staff officers including the future emperors Claudius II and Aurelian in the summer of A. D. 268. They elevated Claudius II to the throne in Gallienus' place.
Many of the early coins of Gallienus are of good silver (about 40%) and of decent workmanship and artistic style. Coins from later in his reign were often dark, irregular, hastily struck, and generally of poor quality with much of the legend off the flan.