The Collapse of the Tetrarchy and the Struggle for Power (305–307 CE)

Diocletian’s Tetrarchy, designed to prevent civil wars and succession crises, quickly unraveled after his abdication in 305 CE, leading to a chaotic struggle for imperial control. Within just two years, Rome found itself fragmented among multiple rival emperors, marking the beginning of the wars that would ultimately lead to Constantine’s rise.

1. The Abdication of Diocletian and the Division of Power (305 CE)

• In an unprecedented move, both Diocletian and Maximian—the two senior emperors (Augusti)—abdicated together, retreating into retirement.
• Their successors, Constantius Chlorus (West) and Galerius (East), were elevated to Augustus.
• To maintain the system, two new Caesars were appointed:
  • Severus (West, under Constantius Chlorus).
  • Maximinus Daia (East, under Galerius).

While this transition initially appeared stable, the system began to unravel almost immediately after Constantius Chlorus' death.

2. The Tetrarchy Unravels (306 CE)

• July 25, 306 CE – Constantius Chlorus dies in Eboracum (modern York) while campaigning in Britain.
• His troops immediately proclaim his son, Constantine, as Augustus, challenging the Tetrarchic system, which had not accounted for dynastic succession.
• August 306 CE – Galerius rejects Constantine’s claim, instead promoting Severus to Augustus of the West.
• October 28, 306 CE – A revolt in Rome leads to the Praetorian Guard proclaiming Maxentius (son of Maximian) as Augustus, further complicating the power struggle.

By the end of 306 CE, the empire was now ruled by five competing claimants:

• Four Augusti: Galerius, Constantine, Severus, and Maxentius.
• One Caesar: Maximinus Daia.

3. Further Fragmentation and the Return of Maximian (307 CE)

• In 307 CE, the political crisis deepened as Maximian came out of retirement, reclaiming the title of Augustusalongside his son, Maxentius.

• With Maximian's return, the empire now had six rulers, further destabilizing the situation.

• Galerius and Severus launched a campaign against Maxentius and Maximian in Italy, but it ended in disaster:

  • Severus was captured and executed on September 16, 307 CE, by order of Maxentius.

• To secure his position, Maxentius arranged a political alliance with Constantine:

  • Constantine married Fausta, Maximian’s daughter and Maxentius’ sister, strengthening ties between the two rulers.

4. The Political Map of the Roman Empire (End of 307 CE)

By the end of 307 CE, the Tetrarchy was in complete disarray, with power divided among:

• Four Augusti:

  1. Maximian (Italy, ally of Maxentius).
  2. Galerius (Eastern Roman Empire).
  3. Constantine (Western provinces, Britain, Gaul, and Spain).
  4. Maxentius (Rome and parts of Italy, self-declared Augustus).

• One Caesar: Maximinus Daia, further signaling the collapse of the once carefully structured Tetrarchy.

5. The Road to Further Conflict (308–324 CE)

• The situation would continue to deteriorate as rivalries deepened, leading to further wars of succession.
• Over the next two decades, Constantine would gradually eliminate his rivals, culminating in the Battle of the Milvian Bridge (312 CE) against Maxentius and his ultimate defeat of Licinius (324 CE), becoming sole ruler of the Roman Empire.

The collapse of the Tetrarchy exposed the inherent flaws in Diocletian’s system, demonstrating that dynastic ambition and military loyalty ultimately dictated imperial succession, rather than any structured administrative plan.

Atlantic West Europe, 304–315: Imperial Reorganization, Persecution, and Early Constantine Era

Political and Military Developments

• Great Persecution and Its Impact

  • Diocletian’s Great Persecution (303–311) severely affected Christian communities in Atlantic West Europe. Significant persecutions occurred notably in cities such as Trier, Lyon, and Poitiers, testing but ultimately strengthening the region’s Christian infrastructure.

• Rise of Constantine the Great

  • In 306, Constantine the Great was proclaimed emperor by his troops in York (Eboracum), Britain, quickly establishing his authority over Atlantic West Europe.

  • Following his victory at the Battle of the Milvian Bridge (312), Constantine began integrating Gaul more firmly into his expanding western empire, initiating significant administrative reforms from Trier.

• Administrative and Military Reforms

  • Constantine expanded and reorganized provincial administrations to improve efficiency and taxation.

  • Strengthened military infrastructure along the Rhine frontier limited Germanic incursions, securing regional stability.

Economic and Social Developments

• Recovery and Prosperity Under Constantine

  • Constantine’s reforms, including monetary stabilization with the introduction of the gold solidus, revitalized trade networks across Gaul.

  • Urban centers like Bordeaux, Trier, Tours, and Poitiers experienced renewed prosperity through improved economic management and imperial patronage.

• Consolidation of Rural Wealth

  • Landholding elites continued to consolidate rural estates, increasing agricultural productivity and economic stability in rural Gaul.

Cultural and Religious Developments

• End of Persecutions and Christian Consolidation

  • Constantine’s Edict of Milan (313) legalized Christianity, facilitating a rapid expansion and institutional consolidation of the faith across Atlantic West Europe.

  • Cities such as Trier and Tours became early episcopal seats, establishing lasting religious infrastructures.

• Rise of Ecclesiastical Influence

  • Bishops gained considerable social influence, becoming key mediators between the imperial administration and local communities.

Significance

The era of 304–315 marked a transformative shift in Atlantic West Europe, characterized by Constantine’s rise and the end of religious persecution. Administrative reforms, economic revitalization, and Christianity’s newfound legitimacy significantly reshaped the region, laying lasting foundations for subsequent centuries.

Galerius, refusing recognition of the imperial claim at the death of Constantius, instead offers Constantine the lesser rank of caesar.

He insists that Severus govern the West, but his protégé’s supremacy is short-lived: the new ruler becomes unpopular when he imposes higher taxes on the people of Rome and of Italy.

Constantine Joins His Father Constantius in the West (305–306 CE)

In 305 CE, following the abdication of Diocletian and Maximian, Constantius Chlorus was elevated to Augustus of the West, while Galerius became the senior emperor (Augustus) of the East. As part of the Tetrarchic system, Constantius now ruled Gaul, Britannia, and Hispania, while Galerius controlled the Balkans and the Eastern provinces.

Recognizing the political and military significance of his son, Constantius requested that Constantine be sent to join him at Gesoriacum (modern Boulogne, France). This move would prove to be pivotal in Constantine’s rise to power.

1. Constantine’s Status Under Galerius

• Constantine had been serving under Galerius in the Eastern court, gaining military and administrative experience.
• As the son of an emperor, he was a potential rival to Galerius and his faction.
• Constantine was aware that remaining too long in the East might jeopardize his future, as Galerius favored his own allies over Constantine.

2. Constantine’s Escape and Journey to the West

• Galerius was reluctant to send Constantine to Constantius, fearing that he might become a threat.
• According to historical accounts, Constantine escaped the Eastern court, possibly by secretly fleeing at night.
• He allegedly disabled or took the horses along his escape route to prevent pursuit by Galerius’ men.
• He traveled across the empire to Gaul, where he joined his father at Gesoriacum.

3. Constantine Joins His Father in Britain

• Shortly after his arrival, Constantius launched a campaign in Britain, aimed at securing Roman control over the northern frontier.
• Constantine accompanied his father on military campaigns against the Picts, further developing his leadership and battlefield experience.

4. The Death of Constantius and Constantine’s Proclamation (306 CE)

• In July 306 CE, Constantius fell ill and died at Eboracum (modern York, England).
• His troops immediately proclaimed Constantine as Augustus, despite the Tetrarchic system, which did not allow for dynastic succession.
• This move challenged the authority of Galerius, setting the stage for a new power struggle in the empire.

5. Conclusion: A Key Turning Point in Constantine’s Rise

• Constantine’s journey to the West was a defining moment that allowed him to escape Galerius’ control and establish himself as a legitimate claimant to the throne.
• His proclamation as emperor in 306 CE triggered a series of civil wars, culminating in his ultimate victory and unification of the Roman Empire in 324 CE.
• This event set the course for Constantine’s eventual conversion to Christianity and the founding of Constantinople, shaping the future of the Roman world.

By securing his place at his father’s side, Constantine positioned himself for greatness, paving the way for his eventual ascendancy as the sole ruler of Rome.

Constantine, after making his way through the territories of the hostile Severus, crosses together with his father to Britain, where they fight a campaign in the north before Constantius' death in a victory over the Picts at Eboracum (present York) on July 25, 306; his troops immediately proclaim Constantine emperor.

A revolt in Rome, led by Maxentius, son of the retired former emperor Maximian, breaks out on October 28, 306.

Severus, at the head of an army previously commanded by Maximian, marches upon Rome from Mediolanum the following spring.

Maxentius, fearing the arrival of Severus, offers to his father the co-rule of the Empire, allowing him to get back his title of augustus; Maximian accepts, and when Severus arrives under the walls of Rome and besieges the city, his men desert him and pass under Maximian.

Galerius invades Italy but is forced to retreat.

The new tetrarchy (two Augusti with a Caesar under each) begins to break down.

Maximian, reclaims the throne to support his son Maxentius' claim to be Caesar, but father and son soon quarrel.