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Jan. 16, 2020

28 – In This Sign You Shall Conquer

28 – In This Sign You Shall Conquer

Galerius rules from the East and Constantine fears for his life. One night the young man flees to Gaul to rejoin his father in the west. When Constantius dies his son becomes emperor. In the chaos that follows the ambitious man looks to the heavens and receives divine revelation.


The year is 305. Galerius has ascended to the position of Augustus and two of his cronies have become the new Caesars. For the time being his only rival in the Roman world was Constantius who ruled the West from Trier. But Constantius was helpless because his 33-year old son Constantine was still a hostage in Galerius’ court. That summer Constantius formally asked Galerius to send his son to Gaul, ostensibly to help him put down a rebellion in Britannia, though his ploy was obvious to everyone. According to Constantine, he was with Galerius at court and after a long night of drinking the Eastern Augustus granted him permission to leave. Constantine left that instant without packing or saying goodbye to friends and comrades. He rode each horse to exhaustion, picking up fresh horses along each waypoint as he fled to the west in case Galerius’ sent assassins after him. That summer Constantine met his father in Bolougne in northern Gaul. He was safe for now, but his future looked bleak.

Constantine had spent over a decade with the retired emperor Diocletian where he learned the art of war and high politics. He was clearly a man of talents, which is why Galerius wanted him dead. But legally he could only climb so high up the Roman political ladder. While his father was the Augustus of the West, Galerius was still the most powerful man in the empire, and even if his Caesars were killed he would just pick new lackies to fill the roles. Furthermore, Diocletian set a precedent that emperors should receive their position through elevation, not inheritance since he believed that hereditary monarchy led to corruption. Constantine wasn’t the only man pushed aside because of Diocletian’s opposition to nepotism. The retired Augustus of the West Maximian tried to elevate his son Maxentius to the role of Caesar but Diocletian vetoed his decision. Even though Constantine was in Gaul, surrounded by his father’s loyalists, his future was still uncertain.

After a brief reunion father and son departed Gaul for Britannia to fight the Picts, which they did for a year. But Constantius fell ill at Eboracum, modern-day York. On 25th July 306 Constantius died, at which point the Roman legions and allied Germans acclaimed his son the new Augustus. As is always the case when the soldiers proclaim a leader it is difficult to say how much of this was planned out by Constantius, Constantine and their loyal officers and how much was a genuine outpouring of love from the legions. Perhaps both occurred; Constantius knew that without an army behind him his son would always be in danger. Meanwhile Constantine had just spent a year valiantly fighting alongside his men while brilliantly commanding them, impressing soldiers and leaders alike. Whether this public show of support was premeditated or not, Constantine clearly deserved his role.

But Constantine knew he couldn’t claim the role of Augustus; to do so was an affront to Galerius’ authority and an act of war. Instead, Constantine sent a message to Galerius asking for his council. He claimed that his soldiers had forced him to become an Augustus and he just couldn’t say, “no;” that would be a total buzzkill, and Constantine was a people-pleaser. When Galerius heard the news he flew into a rage because of the outright insubordination but also because he knew Constantine put him in a delicate position. Constantine showed deference to Galerius so if the Eastern Emperor launched a war he would be seen as the aggressor and a tyrant. If only Constantine had claimed the role then Galerius could have declared war to defend the empire, but the young man had learned high politics from the best.

Furthermore, while Constantine was one emperor out of four his position was far more secure than that implies. Even though his territories were relatively poor and less populated he had arguably the best army in the entire Roman world. He had the veteran Rhine legions and numerous Frankish troops, both of which were legendary warriors. And when Constantius died his old German allies on the other side of the Rhine declared their support for his son. Finally, a century of Germanic raids meant that Gaul was littered with fortresses for Constantine’s forces to retreat to. If Galerius wanted to unseat the upstart emperor he would be in for a rough fight, especially because he could never commit his full forces since he had to defend the eastern frontier from Persia and the Danube from the Goths.

With all of this in mind, Galerius decided to make lemonade out of lemons: he sent Constantine purple robes, conferring emperorship upon him. But Constantine wasn’t going to be the new Augustus since there was already a Caesar, Valerius Severus. Severus would be elevated to Augustus and rule Italy, Hispania and Africa while Constantine was Caesar of Gaul and Britannia. Constantine agreed and the two settled in to an uneasy truce. No doubt Galerius was waiting and plotting for how to eliminate Constantine and make himself undisputed ruler of Rome while Constantine was waiting and hoping for some opportunity to secure himself against inevitable conflict.

In the meantime, Constantine set about proving his right to rule. During his time in Britannia two Frankish chieftains of the Bructeri tribe crossed the Rhine and raided southern Gaul. Constantine raced to Gaul, crushed the invasion and captured its two leaders who he fed to lions in the amphitheater at Trier. Then he went on a punitive expedition against the Bructeri. He captured their adult men and offered them the choice to join the Roman army. Those who refused were fed to wild beasts for entertainment. After successfully defending the frontier Constantine sponsored building projects across Gaul and proved himself as a competent ruler, much to Galerius’ annoyance.

But if Galerius thought Constantine was his worst problem he was in for a shock. The retired emperor Maximian’s son Maxentius watched these events unfold from Rome and was understandably furious. After all his father was the original Western Augustus who had acclaimed him his successor way back in 289 before Diocletian nullified the proclamation. In that time Constantius and Severus assumed that role, Constantine was next-in-line and Maxentius was a nobody. The thirty-year old former heir to the throne schemed and raged alongside his father Maximian, who had unwillingly resigned from his position and was angling for a return to power now that Diocletian had retired to a villa to grow cabbages.

Their moment came in late October when news arrived that Augustus Severus was planning on lifting the tax exemptions on the city of Rome. I mentioned in the previous episode that Diocletian lifted the special status of Italy proper, but this did not include the city of Rome. Rome was still probably the most populous city on Earth with incredible wealth and power. Severus’ plan to raise taxes was scandalous by itself, but this outright rejection of Rome’s specialty was a horrendous affront to a city that claimed to be the center of world civilization, the birthplace and foundation of the Roman Empire and holiest place on Earth. The Romans revolted against their new Emperor and on 26 October, 306 the city garrison proclaimed Maxentius Augustus. In short order central Italy, southern Italy and Africa declared for Maxentius and his father Maximian who joined the rebellion. Severus was caught completely off-guard from his palace at Mediolanum, modern-day Milan, when he heard he had lost half of his holdings and now only controlled northern Italy, Hispania and Pannonia while a disinherited princeling now held the Eternal City and declared him illegitimate.

Severus gathered his armies and marched against Maxentius. But the legions under his command had served under Maximian, who they revered as the human equivalent to Hercules. They defected en masse to his son and Severus was captured and executed in 307. After this Maxentius and Maximian knew Galerius would attack and they decided to forge an alliance with Constantine. Maximian offered Constantine his daughter Fausta to wed and they agreed to recognize him as an Augustus. Constantine agreed, though he largely kept out of wars in the east as he preferred to bide his time and quietly increase his power.

Galerius couldn’t sit back now that another pretender seized power. He assembled his armies and marched into Italy, possibly going as far as Rome itself before he was repelled. Bitterly, the eastern ruler had to accept Maxentius as an emperor. Though even as Galerius was coming to grips with Maxentius’ rule, Maximian was not and he still pined for his old position as Augustus of the west. In April 308 he entered his son’s palace, claimed that he was the rightful Augustus, and that his son should submit to him. What followed may have been one of the most awkward moments in history as the soldiers looked at the old man like he was crazy and didn’t cross over to his side. Maximian was an old man who had been in retirement for years while his son was a young, capable commander who just defeated the Eastern Emperor. After this cringe-worthy coup failed before it started, Maximian fled to Gaul and Constantine’s protection, making things even more awkward as he pleaded with his new son-in-law to protect him from his murderous son. And you thought your family reunions were uncomfortable.

The large-scale bureaucracy of this period means that we have numerous sources on what is happening, though without diaries, letters or other personal records we know very little about the emotional outlook of the people in charge. I wonder if Galerius was thinking less about securing his own power and instead was thinking of securing the Roman Empire from a second crisis period. His attempts at empire-wide governance had failed so he decided to turn to the one man with the wisdom and gravitas to create a new order. In November he called Diocletian out of retirement to preside over a conference at Carnuntum in Pannonia. This conference gave Constantine Hispania and elevated a new man, Licinius, to emperor of Pannonia, meaning five men now ruled the empire. This conference largely affirmed the status quo with one exception: it demanded that Constantine call himself Caesar, not Augustus. Constantine refused this demotion. At this point he had roughly the same territory as Galerius and far more than the other emperors. Galerius referred to Constantine as Caesar for two more years before giving up and admitting that he was an Augustus.

But while everyone else accepted Constantine was the Western Augustus, Maximian still couldn’t stand being pushed aside. He had been worshipped as a living god, and Hercules no less, one of the coolest gods. People had to prostrate themselves before him and his every proclamation was law across hundreds of miles. That’s a hard thing to give up and Diocletian should have recognized that once you make a man the center of an empire most won’t want to retire to the countryside to pull weeds. After arriving in Gaul, Constantine gave his father-in-law command of a few units in order to pacify his need for authority and retain his support. But this wasn’t the same for the old man who hatched a scheme to seize power while Constantine was on the other side of the Rhine fighting the Franks, though this ‘rebellion’ was even more cringeworthy than the last.

In 310 Maximian was stationed in Arles when he proclaimed that Constantine had died in fighting and therefore he was the new emperor. This didn’t make any sense to the soldiers who I imagine shared an awkward laugh and a sidelong glance at their comrades as if to say, “is this really happening?” First, no one had received any word that Constantine had died or that the Rhine campaign was going poorly. Second, Maximian wasn’t chosen as a successor by Constantine and had little support among the army since most had never served under him. Third, Constantine already had a son, Crispus, who was next in line. Fourth, there were a number of far more popular generals in Gaul that could gain more support for their claims, but they remained loyal to Constantine. As the soldiers started walking away from the crazy old man he started offering them cash but this desperate act only made things worse. Humiliated, Maximian fled from Arles to Masillia where he prepared for Constantine to besiege the city. But when Constantine arrived at the head of a massive army the city’s guards just opened the gates. Constantine cornered the old man and essentially said that he could either kill himself or be executed. Maximian knew his time had come and hanged himself in July 310. He had once been a great general and the brutal savior of Gaul, but he had always been a terrible politician.

Constantine was now in a very awkward position. He had based his claim to Augustus on the acclimation of Maximian, who he had just sort-of-but-not-really killed, and Maxentius, who called him a murderer and illegitimate. Moreover, Maximian had been worshipped as the earthly equivalent to Hercules and Constantine pushing him to suicide was still an affront to the Roman religion. Thus, Constantine’s rule went against the entire Tetrarchic political and religious system. Constantine recognized this and on 25 July 310 he laid out a whole new basis for his rule. He claimed that right to rule was hereditary and revealed that he was descended from Cladius II and therefore was part of a long imperial tradition. Then he broke with Roman state religion which purported that Jupiter and Hercules had chosen their representatives, by claiming that the gods Apollo and Victoria, goddess of Victory, had granted him dominion over the whole Earth.

But Constantine soon realized that he couldn’t just reinterpret Roman polytheism; he had to undermine it to legitimize his rule. He soon exchanged worship of Apollo with the cult of the sun god Sol Invictus. Sol Invictus was a popular god outside of the traditional Roman pantheon, and his henotheistic cult was previously promoted by emperor Aurelian. Unlike polytheists who worshipped many gods, or monotheists who believed in one, henotheists admitted there were other gods but reserved worship for one. Sol Invictus was the great god who gave life and light to the world and presided over all things, while all other gods were either manifestations of him or lesser than him. It’s hard to tell what Constantine truly believed; considering that he proclaimed he was chosen by Apollo, then dropped Apollo in favor of the more politically-suitable Sol Invictus, Constantine may have just believed whatever would give him power. But this transition was an important one. Constantine’s belief that old Roman polytheism undermined his reign and that he had to promote a new religion would have an enormous impact on later developments. In the West, Sol Invictus was probably the most popular mystery cult. In the East, Christianity was easily the largest religion outside of Roman polytheism. And since Sol Invictus was the Unconquered Sun and the God of the Bible claimed that he was light and life, it was an easy thing to transition from one god to another.

The Roman world was a four-way chessboard and the rules were constantly changing. In 310 Galerius fell deathly ill and died the following Spring. His last act was to end the persecution of Christians though this didn’t stop later propaganda that he was a sadistic tyrant that God struck down. With the senior Augustus of the East dead, Licinius took control of Eastern Europe while Maximin Daia controlled the Asian dioceses. Maximin Daia resented Galerius’ favoritism towards Licinius and his sudden acquisition of territory, leading to a period of unease. Constantine took advantage of this and allied with Licinius in order to surround Maxentius.

At this point Maxentius’ rule was falling apart. Like so many politicians throughout history he had won his office by opposing taxes only to discover upon taking office that taxes were necessary to keep society going. After all, roads, public buildings, civil services, the military, food imports and other necessities don’t just come from nowhere. Rome in particular was Maxentius’ big problem. Rome could swell to over a million people when it had an entire empire feeding it, but Maxentius only controlled Italy and northern Africa, the latter of which was in constant revolt. Maxentius was forced to raise taxes, infuriating the privileged Romans and Italians. Maxentius knew he needed to conquer more territory or be overthrown. Licinius’ had fought Maxentius to a standstill, which convinced Maxentius he had to try his luck fighting Constantine.

Maxentius had a number of excuses to declare war on his rival Western ruler. Constantine had pretty much killed his father; nevermind that Maxentius was planning on doing the same thing. Constantine waged a propaganda war calling him illegitimate even as Maxentius labelled Constantine a murderer. The breaking point came when Maxentius learned about the alliance between Constantine and Licinius. Furthermore, when Maximin Daia learned about this alliance he was furious and allied with Maxentius. Thus the Roman world was split between warring emperors in the West and East and Maxentius declared war on Constantine in late 311 and waited for spring to come so he could launch an invasion of Gaul.

Before Maxentius could act, in early Spring, Constantine crossed the Alps and took Susa. Then Constantine engaged Maxentius at Turin and handedly defeated him. These two victories made many cities in northern Italy swear fealty to Constantine, and after a few more battles in the north he was free to march upon Rome. Maxentius went into full retreat to Rome where he ordered all bridges leading into the city to be cut and bunkered down for a siege, leaving central Italy undefended. Naturally, the cities of central Italy swore for Constantine as he passed through with his army.

As Constantine neared the city, Maxentius suddenly changed tactics; rather than hiding behind the Aurelian Walls with his large stores of grain to wait out Constantine, he decided to meet him in pitched battle. There are many possible reasons: one was that if Maxentius holed up in Rome, Constantine could continue to conquer more territory until Rome was all he had left. Another was that Maxentius was very unpopular in Rome and feared that if he stayed while Constantine won victory after victory someone would assassinate him. One source holds that Maxentius asked his soothsayers to interpret the will of the gods and they led him to believe that a battle needed to take place, rather than a long siege. Regardless of why, Maxentius decided to repair one bridge and march out to meet Constantine.

Long after the battle took place Constantine claimed that on 27th October 312, as his armies were within marching distance of Rome, he had a dream. In the dream he gazed up at the sun and saw a holy light, then heard a voice saying, “In this sign you shall conquer,” and in the morning he ordered his men to paint the symbol he saw on their shields. Ancient sources are unclear as to what he saw, with some saying it was the Latin cross, others claiming it was the Chi-Rho symbol that early Christians used to denote Christ. Modern historians have pointed out that even a year after the battle Constantine still depicted himself on coins as Sol Invictus, so the sign might have been a halo or some other symbol relating to the sun. Constantine’s later propaganda claims he met Christ in a vision and used a Christian symbol, though this doesn’t explain why he still fashioned himself after Sol Invictus. It is also possible that none of this happened at all and it was all made up long after the fact; Constantine developed an enormous list of outright lies stemming from his youth to his seniority about unbelievable deeds he accomplished and miraculous happenings around him, which he used for propaganda. We may never know what happened the night of October 27th, but we certainly know what happened the following morning.

Maxentius positioned his men too close to the Tiber River so when Constantine outmaneuvered him and pushed his armies backward they had nowhere to retreat to and many were pushed into the river and drowned in their heavy armor. Retreat was impossible as only one bridge remained, and even that collapsed under the onrush of panicked soldiers. Maxentius drowned in the Tiber and his men were captured or slaughtered. Maxentius’ body was recovered and his head was placed on a spike and carried like a banner beside the victorious Constantine. On 29th October Constantine entered the city and soon thereafter all of Rome and Hispania pledged loyalty to him. Africa held out until Constantine sent them the old emperors’ head, at which point they submitted as well. In short order Maxentius’ dioceses surrendered and Constantine became the undisputed emperor of the West.

In February 313 the Western Emperor met Licinius at Mediolanum where the two discussed the new Roman order. Constantine offered his sister to Licinius and they renewed their alliance. But of all their agreements the most well-known to history is the so-called Edict of Milan. This edict granted tolerance to all religions, though since Christianity was the one that had experienced the most recent and most vigorous persecution both parties knew this was directed specifically at them. Moreover, all land seized from Christians by Diocletian were to be returned. This was a momentous shift in Roman culture. For so long Roman polytheism smashed any religion that couldn’t be incorporated, whether it be the druids of Gaul, the brutal persecutions of Jews under Titus, and so often the Christians.

At this point, Christians represented roughly 10% of the empire’s population and so Constantine couldn’t openly come out as a Christian, if he even was one. But the Edict of Milan allowed Christianity to spread and as it did Constantine’s reputation soared among the faithful who looked to him as God’s chosen. I’ll have more to say on this when we discuss Christianity, but since we are talking high politics in this episode just know that Constantine’s popularity grew across the empire and especially in the East due to this edict.

Speaking of the East, as Licinius met with Constantine Maximin Daia invaded Eastern Europe. Licinius turned about and handedly defeated him, becoming the sole emperor of the East. While Constantine and Licinius claimed that they shared joint rule of a united empire the next eleven years were one of constant tension between East and West, and in 316-317 the two went to war over Eastern Europe. During this war Constantine’s Franks met Licinius’ Goths and the former proved their worth. By 317 Constantine ruled all of Europe except Thrace, and Licinius was caught between Constantine and Persia.

That year both emperors named their sons as heirs, formally ending meritocratic elevation in favor of dynasties. In 320 Licinius resumed persecution of Christians in his territory, most likely because they favored Constantine, and because he wanted to seize their wealth to replenish his coffers. In 323 Constantine launched a war against Licinius and within a year had won control of the entire Roman world. Constantine ruled from 324-337 as the unchallenged master of the empire.

Constantine’s reign was relatively peaceful, though it was hardly prosperous. Consistent civil wars led to runaway inflation and silver coins were replaced with bronze. There’s a lot more that can be said about Constantine’s work across the empire but most of it didn’t involve Gaul and this is a French history podcast so it doesn’t concern us.

I’ll end this episode by answering the question: what impact did Constantine have on Gaul? More than anything, Constantine sped up the transition from a Romano-Celtic Gaul to Frankish Gaul. Constantine continued his father’s work of replenishing Gaul’s population with Germans to bolster his armies and pay taxes. Constantine used these taxes to fund building projects, pay civil servants and otherwise improve Gaul. But Gaul continually lost its Celtic identity as more Franks were allowed in or forcibly resettled west of the Rhine. Moreover, Constantine’s frequent wars with the other Tetrarchs meant more Franks were taken westward.

This mass migration was not necessarily good or bad, but different. It meant Gaul was more populous, prosperous and well-defended but culturally it was drifting apart. One thing that was particularly dangerous was that many Frankish commanders held dual ranks within Roman armies and within tribal armies. This dual-loyalty wasn’t a problem when the legions were strong and the Franks were satisfied, but these semi-foreign armies within the Roman borders presented a significant threat to Rome in the future.

Gaul was the centerpiece to Constantine’s early empire and he devoted most of his energies to rebuilding it. But by 324 he was master of all of Rome and that year he made a world-changing decision: he decided that the Roman Empire needed a new capital. Rome was corrupt, decaying, and filled with connivers and pagans. Constantine wanted a fresh capital and chose to found Constantinople in the Eastern Empire which was wealthier and more Christian. As Constantine moved east so did the empire’s wealth, civil service, armies and priorities. Even the language of the empire started to change. In the West, the Germanic invasions undermined the Latin-speaking population, while the sudden influx of people to the East, most notably around Constantinople, meant that Greek was becoming more important.

Constantine’s decision to reorient the Roman world eastward was a momentous blow to Gaul. Rome may have been the heart of the old Roman Empire, but Gaul was its shield. For nearly four centuries Gaul was the frontline that separated the ‘civilized’ Roman world from the endless hordes of migrating barbarians. Constantius and his son Constantine believed that Rome was no longer capable of holding a hard border and instead had to have a semi-porous border, and it is under their forty-year reign that the Franks established an enormous, lasting presence within Gaul. Yet, as Constantinople rose to unparalleled glory the holes on Rome’s western frontier widened until eventually there wasn’t any line of defense against the Germanic invaders. Constantine may have saved Gaul in the short-term, but his prioritization of the East, combined with his settling of Franks created a dangerous situation. It was possible that a day would come when a wealthy emperor in the East would watch the relatively impoverished Gaul fall to hordes of barbarians and decide that it wasn’t worth defending. One day, the prosperous Eastern Roman Empire might abandon Gaul to its fate, and doom the entire Western Empire.



Corcoran, Simon, The Empire of the Tetrarchs: Imperial Pronouncements and Government AD 284-324, 1996.

Ed. David S. Potter, A Companion to the Roman Empire, 2006.

Elton, Hugh, The Roman Empire in Late Antiquity: A Political and Military History, 2018.

Drinkwater, J.E., Roman Gaul, 1983

Gregory of Tours’ The History of the Franks

Heather, Peter, The Fall of the Roman Empire: A New History of Rome and the Barbarians, 2005.

Herodian’s History of the Empire from the Death of Marcus

Mary T. Boatwright, Daniel J. Gargola, and Richard J. A. Talbert, Romans: From Village to Empire, 2004.

Mitchell, Stephen, A History of the Later Roman Empire, AD 284-641: The Transformation of the Ancient World, 2007.

Sessa, Kristina, Daily Life in Late Antiquity, 2018

Williams, Stephen, Diocletian and the Roman Recovery, 1985.