Thread by @StilichoReads

The garrison of Roman Britain, far from the eyes of the emperor and his staff, was notorious for producing coups and usurpers. The final one, in the early years of the 5th century, led to a common soldier becoming emperor and Rome abandoning Britain. Thread:

In 406, the Roman Empire's borders were imploding. In 376, the Goths crossed the Danube, defeating and killing the Emperor Valens at Adrianople. Although they signed a peace treaty and were brought into the Roman army, they were uneasy under Imperial authority.

In 406, another Goth, Radagaisus, invaded Italy. With an army of 100,000 (although this probably includes women and children) he promised to sacrifice the Roman Senate to his pagan gods. His men sacked their way through Noricum and northern Italy.

The emperor at the time was nominally the twenty year old Honorius, but real power was held by his half-Vandal General Stilicho. To deal with these threats, he pulled soldiers off the frontiers to use as a mobile fire brigade, rushed to wherever the threat was greatest.

This caused vast resentment in the frontier provinces. The ordinary low level barbarian raiding had never stopped, but now the army wasn't there to stop it. Many soldiers hated being sent far from their homes and families as well.

Because of this, and probably also problems with their pay, the British army revolted in July 406, proclaiming Marcus as their emperor. Marcus was probably Comes Britanniae, commander of the British field army, or commander of the units that guarded the coasts or Hadrian's Wall.

For whatever reason, the soldiers mutinied and killed him in October 406. They then elevated a local civilian urban official, Gratian as their new emperor. All of them would have known that the loyal Gallic field army, which vastly outnumbered them, would soon come for them.

Then, on the cold New Year's Eve of 406, an army of Vandals, Alans, and Sueves, flooded over the Rhine. Facing no resistance for unknown reasons, they sacked city after city and threatened the ports that supplied Britain. The rebel soldiers wanted to cross over and fight them.

When Gratian refused, they killed him too in early 407. They then chose a common soldier, Constantine, as their new emperor, believing that he would be a good ruler because he was named after the previous Emperor Constantine. Constantine would become known as Constantine III.

We don't know much about Constantine III's background, but it is said he was a capable soldier and he may have at least been a junior officer. He was at least old enough to have an adult son when he was proclaimed emperor.

Constantine moved quickly, taking his army across the channel at Boulogne. The Gallic and Spanish field armies both declared for him and he led his troops against the Vandals, defeating them multiple times and stabilizing the frontier.

Stilicho, who defeated and killed Radagaisus, now turned his attention to Constantine. He sent an army under a Gothic chieftain, Sarus, into Gaul. Sarus met one of Constantine's generals, Iustinianus, in battle and killed him. He then killed another, the Frank Nebiogastes.

Sarus managed to corner Constantine in the city of Valence and put it under seige. However, Constantine's new generals, Gerontius and Edobichus, arrived to relieve him and forced Sarus to retreat back into to Italy. Constantine had fully secured Gaul and made Arles his capital.

Hispania was a loyalist stronghold, ruled by cousins of Honorius. The nightmare scenario for Constantine was therefore a two pronged invasion, with one Imperial army coming from Italy and another from Spain. He knew had to knock them out one at a time.

To do this, he pulled his son, Constans, out of a monestary and made him junior emperor in 408. He then sent Constans and Gerontius into Hispania, where they easily defeated Honorius' cousins. Constans returned to Gaul, leaving behind Gerontius to govern from Saragossa.

Before the British rebellion, Stilicho had been engaged in negotiations with the Visigothic King Alaric for a joint attack on Illyria. When Stilicho's priorities shifted for obvious reasons, Alaric demanded the gold he was promised anyway, threatening to attack Italy.

Stilicho wanted to make the payment, angering many senators and officers. In August 408, the Italian field army mutinied, killing many officers loyal to Stilicho. Stilicho, not wanting to start another civil war, willingly handed himself over to be executed.

Local Romans hunted down and killed the families of Germanic Roman soldiers in the aftermath, causing many to desert. Alaric's army swelled with these men, as well as those who had been loyal to Stilicho. Honorius had no army with which to oppose him as he marched on Rome.

Desperate, he sent envoys to Constantine, offering to make him co-emperor in 409. Constantine agreed, but before he could take his army into Italy the Vandals, never fully subjugated, attacked south into Hispania, and he sent Constans to deal with them.

Gerontius, still governing Spain, then revolted against Constantine, proclaiming his relative (possibly son) Maximus as emperor and marching north into Gaul. The noose was tightening around Constantine and his new regime.

In Britain, Saxon raids along the coasts continued, and the province now resented Constantine for taking their army to the continent much as they had resented Stilicho before. They threw off imperial authority; it would never return to the island.

In one last desperate gamble, Constantine was invited into Italy by the opponents of Honorius. Honorius was weak and ineffectual; if he was replaced by a strong emperor with a military background, the empire's resources could be fully mobilized against its many threats.

However, Constantine lacked enough soldiers and was quickly forced to retreat in the spring of 410. At the same time, Alaric continued his war on Honorius, ultimately sacking Rome in August when Honorius refused to pay him off.

Gerontius advanced deeper into Gaul. When Constans led an army against him, he defeated him, captured him, and killed him. He laid siege to Constantine in Arles, but Constantine held out hope - his surviving loyal general, Edobichus, was raising a relief army amongst the Franks.

Honorius finally had a stroke of luck, finding a competent and loyal general, Constantius. Constantius led an army into Gaul, defeating Gerontius, who committed suicide in the aftermath. He then ambushed and destroyed the Franks under Edobichus.

Constantine, realizing the game was up, surrendered and agreed to become a priest. However, Constantius went back on his promise of safety and had him killed. The general would go on to stabilize the empire and become emperor himself - but he will be left for my next thread.