The period between 337 and 350 AD in the Roman Empire was marked by fierce internal strife, dynastic purges, external warfare with Persia, and a series of emperors whose reigns dramatically shaped the late Roman world. This era saw the violent suppression of Constantine the Great’s heirs, military confrontations with the ambitious Persian King Shapur II, and the turbulent rise of new leaders including Magnentius and Julian. Understanding these events is vital to grasp how the Roman Empire navigated the challenges of political fragmentation and external threats during the mid-fourth century.

The Aftermath of Constantine the Great’s Death: A Dynasty Under Siege

When Constantine the Great died in 337 AD, the Roman Empire he had unified under his rule was suddenly vulnerable. The emperor’s body had barely been laid to rest when conspirators set about dismantling his legacy by targeting his family. Soldiers, manipulated by political scheming, insisted that only Constantine’s sons could legitimately inherit the empire. This led to a brutal purge that decimated the imperial family.

Two of Constantine’s nephews, Dalmatius and Hannibalianus, were imprisoned but later released upon the arrival of Constantius II, one of Constantine’s surviving sons. Constantius II pledged to protect the royal lineage, yet the atmosphere of suspicion and betrayal quickly escalated. Soldiers clamored for the execution of members of the imperial family, culminating in a massacre that claimed the lives of Constantius II’s two uncles, seven cousins, and his relative, Optatus. Even Constantine’s trusted official, Ablavius, was not spared.

After this violent purge, only two of Constantine’s grandsons remained: Gallus, son of Julius Constantius, and Julian, also known as Julian the Apostate. This ruthless internal cleansing significantly narrowed the succession line and set the stage for future power struggles among the surviving heirs.

The Division of the Empire and the Tripartite Rule

In September 337, the three surviving sons of Constantine—Constantine II, Constantius II, and Constans—met secretly to negotiate the division of the empire’s vast territories. They agreed to a new power-sharing arrangement that acknowledged the eldest, Constantine II, as the primus inter pares . This tripartite rule was intended to maintain unity but sowed the seeds for future conflicts.

Constantius II took charge of the Eastern provinces, a region brimming with challenges and threats, particularly from the Sasanian Persian Empire. Constantine II controlled the Western provinces of Gaul, Britain, and Spain, while Constans governed Italy, North Africa, and the Balkans. This arrangement, though seemingly balanced, was fragile and marked by underlying tensions that would soon erupt into open conflict.

The Persian Wars: Shapur II’s Ambition and Rome’s Struggles

During this period, the Roman Empire faced a formidable adversary in the East: Shapur II, the Sasanian king of Persia. Shapur II was a dynamic and ambitious ruler who sought to reclaim territories lost to the Romans under Emperor Galerius decades earlier. He had long been deterred by Constantine the Great’s military prowess but saw new opportunity as the empire was now led by less experienced and younger emperors.

Shapur launched a series of invasions into Mesopotamia, an area of strategic importance. The Roman chronicles from these years are filled with accounts of defeat and hardship. The Roman legions suffered numerous setbacks and towns fell under Persian siege or occupation. However, in 348 AD, in the Battle of Singara, Constantius II managed a significant victory, routing the Persian forces.

Despite this success, the Roman army’s eagerness for plunder led to a disastrous lapse in discipline. Against Constantius’s orders to halt the attack at nightfall, the soldiers pressed their assault, seizing the Persian camp and looting. Taking advantage of the chaos, Shapur II’s forces counterattacked from nearby hills under cover of darkness, inflicting heavy casualties on the scattered Roman troops and forcing a painful retreat.

This battle was reportedly Shapur’s ninth victory over Roman forces during his campaigns. Nevertheless, the Persians were unable to capture the key fortified city of Nisibis, which withstood three separate sieges due to the valiant defense of Roman soldiers and skilled engineers. Nisibis remained a critical bulwark against Persian expansion.

The Western Empire Under Constantine II and Constans: Fraternal Rivalry and Civil War

While Constantius II was preoccupied with the East, the Western empire saw its own turmoil. Constantine II demanded the transfer of the African provinces from Constans. Dissatisfied with Constans’s perceived insincerity during negotiations, Constantine II resorted to military action in 340 AD.

Constantine II’s campaign against Constans ended abruptly near Aquileia, where he fell into an ambush and was killed in battle. This sudden death allowed Constans to consolidate control over the entire Western Roman Empire. He refused any territorial concessions to Constantius II, who, notably, made no claims for himself during this reorganization.

The Decline of Constans and the Rise of Magnentius

Constans’s reign over the West lasted another decade but was marked by increasing neglect and unpopularity. He indulged in hunting and other pleasures, alienating many within the military and the court. This dissatisfaction culminated in a coup in 350 AD led by Magnentius, a Frankish-born officer commanding the Jovians and Herculians legions.

Magnentius capitalized on a grand banquet held under the pretense of celebrating his son’s birthday. As the festivities reached their peak, Magnentius dramatically appeared in imperial purple, declaring himself emperor. His supporters, including key military officers, quickly hailed him, and the ranks soon followed suit. Magnentius promised reforms and a more attentive rule, appealing to those disillusioned by Constans’s leadership.

Gallus and Julian: The Remaining Members of the Imperial House

The aftermath of the purges and political upheavals left Gallus and Julian as the last surviving male members of Constantine’s family. Gallus was appointed Caesar and governed parts of the Eastern provinces but was later executed on Constantius II’s orders amid suspicions of disloyalty.

Julian, initially sidelined, eventually rose to prominence, especially during his service in Gaul. He distinguished himself through military successes against Germanic tribes, earning the loyalty of his troops. His leadership culminated in the crucial Battle of Strasbourg in 357 AD, where he decisively defeated the Alemanni confederation, securing the Rhine frontier.

Following this victory, Julian was acclaimed emperor by his soldiers, a direct challenge to Constantius II’s authority. His rise marked a turning point in the empire’s internal politics, setting the stage for the eventual transition of power.

The Death of Constantius II and the End of the Triumvirate

Constantius II continued to rule the Eastern Roman Empire, engaged in both Persian warfare and managing internal affairs. However, his reign was plagued by ongoing conflicts and the looming threat of usurpers.

In 361 AD, Constantius II died while campaigning against Julian, who had been declared Augustus by his troops. With his death, Julian became the sole emperor of the Roman Empire, ending the complex and often violent power-sharing arrangement that had dominated the previous decades.

Conclusion: Legacy of an Era Defined by Turmoil and Transition

The years between 337 and 350 AD represent a critical juncture in Roman history. The violent purge of Constantine’s heirs demonstrated the brutal nature of imperial succession and the fragility of dynastic rule. The persistent wars with Persia under Shapur II underscored the empire’s vulnerability to external threats, even as internal divisions weakened its capacity for unified defense.

The rise of Magnentius and later Julian highlighted the ongoing struggle between military power and dynastic legitimacy. Julian’s eventual ascendancy not only restored a semblance of stability but also foreshadowed significant religious and administrative changes that would impact the empire’s trajectory.

This era’s dramatic episodes of betrayal, warfare, and political intrigue reflect the complexities of governing a vast and diverse empire under pressure from both within and without. The legacies of these tumultuous decades continue to captivate historians and readers interested in the resilience and challenges of the late Roman Empire.