Gallienus

• 1. Introduction

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  Gallienus ruled Rome for fifteen years, the longest reign in half a century, and spent nearly every one of those years fighting. He fought Germanic tribes on the Rhine, Persian-backed usurpers in the East, breakaway generals in Gaul, and a cavalry commander right outside Milan. He won most of those fights. He still could not hold the empire together.

  Born around 218, Publius Licinius Egnatius Gallienus came from a wealthy senatorial family with roots in Falerii in Etruria. His father Valerian became emperor in September 253 and immediately made Gallienus his co-ruler with the title Augustus. From that moment, the two men divided the world between them: Valerian went east to hold back Persia, while Gallienus stayed west to keep the Germanic tribes off the Rhine and the Danube.

  For seven years that arrangement held, more or less. Then, in 260, Valerian was captured by the Sassanid ruler Shapur I at the Battle of Edessa. No Roman emperor had ever been taken prisoner by a foreign enemy. The empire fractured almost at once. Two breakaway states formed. Usurpers rose in nearly every province. The man who had to reassemble all of it was Gallienus, alone, with no father to share the burden.

  How he managed, what he changed, and why the ancient sources despised him even as they recorded his victories, is the story that follows.

• 2. The Divided Empire

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  Valerian's decision to split the empire was not sentimentality. The sheer scale of Rome's territory, combined with the volume of simultaneous threats, made a single command center impossible to sustain. Enemies on the frontiers demanded to deal directly with the emperor; a distant letter from Rome carried no weight the way an imperial presence did.

  Gallienus took the western half. Between 253 and 258, he spent most of his time in the Rhine provinces, cycling through Germania Inferior, Germania Superior, Raetia, and Noricum. Ancient writers Eutropius and Aurelius Victor credit him with particular energy in keeping invaders out of the German provinces and Gaul, even when Valerian's earlier march against a rival had stripped troops from the frontier.

  Coins minted during this period record multiple victories, including what may have been a win in Roman Dacia, though the precise date is uncertain. In 255 or 257, Gallienus was made consul again, which suggests at least a brief return to Rome on those occasions, though no written record survives.

  During a Danube campaign, Gallienus elevated his elder son Valerian II to the rank of Caesar, making the boy the formal heir to both himself and Valerian I. When Gallienus moved west to the Rhine in 257, Valerian II stayed behind on the Danube as a symbol of imperial authority. That boy most likely died in 258, possibly caught up in the chaos of the first major usurpation.

• 3. The Year Everything Broke

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  Sometime between 258 and 260, the governor of at least one Pannonian province, a man named Ingenuus, declared himself emperor. Gallienus reacted with striking speed. He left his youngest son Saloninus at Cologne under the supervision of an officer named Albanus (or Silvanus), then crossed the Balkans with his new cavalry corps, the comitatus, under the command of Aureolus. Gallienus defeated Ingenuus at Mursa or Sirmium; Ingenuus died there, either killed by his own guards or drowned in flight.

  Almost simultaneously, an Alemanni invasion poured through the Roman frontier, possibly because the troops who had accompanied Gallienus north left a gap in the defenses. Franks broke through the lower Rhine and drove as far as Tarraco in southern Spain. The Alemanni themselves pushed through the Agri Decumates and ravaged Germania Superior and Raetia before entering Italy proper. It was the first invasion of the Italian peninsula since Hannibal, nearly five centuries earlier.

  When the invaders reached the outskirts of Rome, the Senate assembled an improvised force of local troops and civilians to push them back. On the retreat north, the Alemanni met Gallienus's army near Mediolanum, present-day Milan, and were decisively defeated. They left the empire alone for the next ten years. The Senate's independent military action, however, planted what one later historian suggested was a seed of jealousy in Gallienus, contributing to his eventual decision to bar senators from military command.

  Then came the blow that eclipsed all the others. In early spring of 260, Valerian's army, already weakened by plague, was defeated at the Battle of Edessa. Valerian was captured. Shapur's forces then swept through Cilicia and Cappadocia, sacking, according to Shapur's own inscriptions, thirty-six cities.

• 4. Rebels on Every Front

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  Control of the whole empire passed to Gallienus in 260, but it was an empire in pieces. In the East, the fiscal official Fulvius Macrianus and his sons Quietus and Macrianus proclaimed themselves emperors. They marched on Europe with an army of thirty thousand men, according to the Historia Augusta, and at first met no resistance. Gallienus sent Aureolus against them; a decisive battle in spring or early summer of 261, most likely in Illyricum, destroyed their army. The two Macriani were killed. Odenathus of Palmyra, who had helped turn the tide against Shapur, was given the title dux Romanorum and subsequently besieged the remaining rebels at Emesa. The people of Emesa killed Quietus themselves; Odenathus arrested and executed Balista in about November 261.

  Around the same time, in the Balkans, a commander named Regalian had also declared himself emperor. The Historia Augusta is almost the only source for these events, and it offers no credible explanation for why Regalian acted. He held power for roughly six months, struck coins with his own image, and won some success against the Sarmatians before the Roxolani invaded Pannonia and killed him at Sirmium. Some historians suspect Gallienus invited the Roxolani to do exactly that.

  In Egypt, the prefect Lucius Mussius Aemilianus had supported the Macriani and then launched his own revolt in spring 262. Pope Dionysius of Alexandria's correspondence captures the atmosphere of that moment: invasion, civil war, plague, and famine layered on top of one another. Gallienus sent the general Theodotus, probably by sea, to deal with Aemilianus. The decisive battle took place near Thebes; Aemilianus was clearly defeated. Gallienus then served as consul three more times, in 262, 264, and 266.

• 5. The Gallic Empire

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  Of all the losses Gallienus suffered after 260, the most durable was the formation of what modern historians call the Gallic Empire. Its founder was Postumus, a general holding the Rhine bank who had been trusted with the defense of the west and the supervision of Gallienus's son Saloninus.

  The sequence of events that produced the break is specific. Postumus defeated some Germanic raiders and distributed the spoils among his own soldiers rather than returning the goods to their rightful owners. When Saloninus's guardian Silvanus demanded the treasure, Postumus appeared to comply but his men mutinied and proclaimed him emperor. They besieged Cologne, and after weeks the defenders handed over both Saloninus and Silvanus. Postumus had them killed. An inscription found in 1992 at Augsburg fixes the date: Postumus had been proclaimed emperor by September 260.

  Despite holding Britain, Spain, much of Gaul, and parts of Germania, Postumus, according to the scholar D. S. Potter, never actually tried to march on Italy or depose Gallienus directly. The two men fought, and Gallienus returned in 263 or 265 to besiege Postumus in an unnamed Gallic city. During that siege, Gallienus was severely wounded by an arrow and had to withdraw. The Gallic Empire outlasted him, surviving until 274, six years after his death.

• 6. Military Reforms

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  Gallienus left a structural mark on the Roman military that outlasted his reign by centuries. He was the first emperor to commission primarily cavalry units, the Comitatenses, as a mobile strategic reserve that could be deployed rapidly to any point in the empire. In an era when threats materialized simultaneously on multiple frontiers, speed of response mattered more than heavy static garrisons.

  The biographer Aurelius Victor records that Gallienus also barred senators from holding military commands. This was not a cosmetic change. Equestrian officers, generally regarded as more reliable and more professionally focused, rose into the positions formerly held by the senatorial class. Modern scholar Pat Southern argues that these two reforms, the cavalry reserve and the exclusion of senators, did more than just help Gallienus survive his own reign. She places him among the emperors most responsible for creating the Dominate, the late imperial system of government, alongside Septimius Severus, Diocletian, and Constantine I.

  The reforms also created a precedent that Diocletian and Constantine I explicitly built on. The Comitatenses became the backbone of the late Roman field army.

  One concrete relic of the Gallienus era surfaced much later in modern times. About forty rare gold coins bearing his image were found as part of what is known as the Lava Treasure, discovered in Corsica, France, in the 1980s.

• 7. Assassination and Legacy

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  In 268, the cavalry commander Aureolus, who had been stationed at Mediolanum to watch Postumus, switched sides and claimed the throne for himself. Gallienus defeated him at what is now Pontirolo Nuovo near Milan, drove him back inside the city, and began a siege.

  He never finished it. Cecropius, commander of the Dalmatian troops, spread a false report that Aureolus's forces were breaking out of Milan. Gallienus left his tent without his bodyguard and was stabbed. Ancient sources agree that most of Gallienus's own officials wanted him dead; the Historia Augusta names Aurelius Heraclianus and Lucius Aurelius Marcianus as the conspiracy's leaders, though the latter's role is not confirmed by any other ancient source.

  On learning of his death, the Senate in Rome immediately ordered the execution of Gallienus's family, including his brother Valerianus and his son Marinianus. The order was only halted when a message arrived from the new emperor Claudius, asking the Senate to spare the family and to deify his predecessor instead.

  Ancient writers were unkind to Gallienus. The Historia Augusta describes him as a lover of luxury who dressed in purple, dusted his hair with gold, and built castles out of apples. Emperor Julian portrayed him in The Caesars walking with the dress and languishing gait of a woman. Modern historians, including Pat Southern, have pushed back. The fifteen-year reign held together, however imperfectly, during a crisis that came close to destroying Rome entirely. His decree of toleration issued after Valerian's capture in 259 was the first official recognition of Christian property rights, restoring places of worship and cemeteries to the Christian community, though it stopped short of making Christianity an official religion. The tomb of Gallienus is believed to lie to the south of Rome, at the ninth mile of the Via Appia.