As I indicated in my previous post, when Constantine had been acclaimed emperor by his troops in Britain (at the city of York) in 306 CE (upon the death of his father Constantius), it was taken as a license for Maxentius to assume power in Rome.   The reason is this.  Diocletian, as we have seen, had tried to move the empire to a new system of governance, the Tetrarchy, in which four leaders, all chosen for their experience and skills, would rule.  When a senior member in the East or West retired or died, the junior Caesar serving under him would be elevated and the senior A Augustus would choose, then, the new junior replacement.

But Constantine was acclaimed – or so it was thought or claimed – not because he had been appointed but because he was the son of the outgoing Augustus.  In other words, his accession came not because of a decision of the Augustus but because of birth.  It was succession by the dynasty principle, precisely what Diocletian had tried to get rid of.  (In fact, it may not actually have been that way; it may be that as the senior Augustus Constantius actually did make the decision before his death. In any event…)

Constantine was not the only son of an emperor who had been passed over by Diocletian’s Tetrarchy.  So had …

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So had Maxentius, the son of Maximian, the co-Augustus with Diocletian.  When Constantine had been elevated to power, Maxentius was not about to put up with it.  And so he arranged for the troops in Rome to declare him too as emperor.  Now there were five rulers instead of four.  And just to complicate matters further, Maxentius called his father Maximian out of retirement (he had not wanted to go in the first place, but Diocletian had insisted).  So now there were six emperors.  Just as soon as Diocletian’s plan for succession had been implemented, it failed miserably.

This proved unacceptable to all the four other emperors (Constantine and Severus in the West and Galerius and Maximin Daia in the East).  It led to civil war.

Galerius was the senior member of the four, and he directed Severus to attack Maxentius.  Severus brought in his troops from the West, but as it turns out, many of them had earlier served under Maximian and still held him in esteem.  During the assault on Rome, many of Severus’s troops deserted to Maximian’s army, and Severus suffered a humiliating loss.  He himself was later forced to commit suicide.  Galerius chose a military man named Licinius to replace him as Augustus in the West.

Galerius then decided to attack Maxentius and Maximian in Rome.   He ended up losing principally because of poor planning.  Galerius – like most of the emperors of that age – had never actually been to Rome, and he didn’t realize just how large a place it was.  The city had been fortified some thirty years earlier with new, major walls by the emperor Aurelian.  Galerius did not bring enough soldiers from the East to carry out an effective siege.  He too had to retreat, and ended up eventually losing his life.

It’s a complicated story with lots more ins and outs.  Other skirmishes happened.  Eventually Constantine confronted Maximian in battle, and Maximian lost and was (permanently) taken out of the equation.

Finally, in 312 CE, Constantine decided to attack Rome.  His stated rationale was that Maxentius had become a tyrant who was ruling the city ruthlessly.  His unstated rational was that he had very high ambitions, and by conquering Maxentius he would extend his rule, so that it entailed not only Britain, Spain, and Gaul, but also Rome, all of Italy, and North Africa.  There was a lot at stake.

Constantine marched his troops from Gaul, over the Western Alps, into North Italy.   At four cities he engages Maxentius’s army in battle and won each time.  He headed south to Rome.  Then came the major event.

Maxentius did one sensible and one utterly foolish thing in preparation.  Sensibly, he destroyed the bridges crossing the Tiber, making it difficult for Constantine to amass a coherent and directed assault.  Foolishly, after taking out the bridges, he went out to meet Constantine’s army anyway, head on.  Bad idea.

We are not sure why Maxentius chose to leave the city.  Neither Severus nor Galerius several years earlier had been able to lay the city under siege, and Maxentius’s stay-at-home tactics in both instances had led to spectacular success.  Why not do the same again?  The sources for the conflict (principally Eusebius) indicate that problems had developed in the city.  The need for taxes (caused in part because the grain supply from Africa was not coming in) led to civic unrest, possibly riots, apparently some misconduct by soldiers involving, not to put too fine a point on it, the slaughter of civilians, Maxentius’s own increasingly profligate ways, and so on.  It may be the Maxentius realized he needed a decisive victory, not a long drawn out siege, if he himself was to survive.

IN any event, there was no way for Maxentius’s army to cross the Tiber, since the bridges were out, so at the site of the Milvian Bridge north of the city, he had a temporary pontoon bridge built.  He crossed it with his army and awaited Constantine.  Constantine and his forces arrived.  Maxentius had a superior army in front of it and no route of escape behind.  The battle itself was an anti-climax.  Maxentius’s forces were routed.  Many of them tried to cross the pontoon bridge to get back to the city walls.  Too many tried.  The bridge collapsed.  Maxentius was on it.  He drowned.

Constantine entered Rome the next day, October 29, 312, as the victor and ruler of the entire Western half of the Empire.  Dead were most of the other emperors: Diocletian, Maximian, Severus, Galerius, and Maxentius.  All that remained with Constantine were Licinius and Maximin Daia.  Before the year was out, Licinius attacked and killed Maximin Daia.  He and Constantine split the empire and ruled jointly for twelve years.  Constantine ended up attacking him as well, to become sole ruler, in 324.

Now, you may wonder what all this has to do with Christianity in Antiquity.  It is this.  It was at the Battle at the Milvian Bridge that Constantine became a Christian.  I’ll explain in subsequent posts.