Constantine III (; died shortly before 18 September 411 AD) was a common Roman soldier who was declared emperor in Roman Britain in 407 and established himself in Gaul. He was recognised as co-emperor of the Roman Empire from 409 until 411.
Constantine rose to power from within the field army of Roman Britain and was acclaimed emperor in early 407. He promptly moved to Gaul (modern France), taking all of the mobile troops from Britain, with their commander Gerontius, to confront bands of Germanic invaders who had crossed the Rhine the previous winter. With a mixture of fighting and diplomacy Constantine stabilised the situation and established control over Gaul and Hispania (modern Spain and Portugal), establishing his capital at Arles. The sitting emperor of the Western Roman Empire, Honorius, sent an army under Sarus the Goth to expel Constantine's forces. After initial victories, Sarus was repulsed. In Hispania, Honorius's relatives rose and expelled Constantine's administration. Constantine raised his oldest son to co-emperor as Constans II and sent him with an army to deal with this. When little progress was made, he sent his general Gerontius with additional troops, after which Constantine's authority was re-established. In early 409 Honorius recognised Constantine as co-emperor. In 409 Gerontius rebelled, proclaimed his client Maximus emperor and incited barbarian groups in Gaul to rise up. Constans was sent to quash the revolt, but was defeated and withdrew to Arles. Meanwhile, Constantine invaded northern Italy, but his plan failed and he also pulled back to Arles. In 410 Constans was sent to Hispania again. Gerontius had strengthened his army with Germanic tribesmen and defeated Constans; the latter retreated north and was defeated again and killed at Vienne early in 411. Gerontius then besieged Constantine in Arles. Honorius appointed a new general, Constantius, who arrived at Arles while Gerontius was outside the city. Much of Gerontius's army deserted to Constantius, who took over the siege. A force attempting to relieve Constantine was ambushed. Constantine abdicated, took holy orders andpromised his lifesurrendered. Constantius had lied: Constantine was killed and his head presented to Honorius on a pole.
Background
Following the death of the Roman emperor Theodosius I in 395 the Roman Empire was divided between his two sons: Arcadius became emperor of the Eastern Roman Empire and ten-year-old Honorius of the Western. Honorius was underage and the leading general Stilicho became hugely influential and the de facto commander-in-chief of the Roman armies in the west.
During this period Roman Britain was suffering raids by the Scoti, Saxons and Picts. Sometime between 396 and 398 Stilicho is said by contemporary poet and speech writer Claudian to have ordered a campaign against the Picts, probably a naval campaign intended to suppress their seaborne raids on the east coast of Roman Britain. He may also have ordered campaigns against the Scoti and Saxons. Other interpretations suggest it went badly, or that troops defending Roman Britain defeated a Pictish invasion without external support. This is the last recorded Roman military campaign in Britain. Stilicho sent funds to strengthen the defences along Hadrian's Wall and the coastal defences at about the same time.
In 401 or 402 Stilicho needed military manpower for wars with the Visigoths and the Ostrogoths and so stripped Hadrian's Wall of troops. The year 402 is the last date from which Roman coinage is found in large quantities in Britain, suggesting the Empire was no longer paying the troops who remained. Meanwhile, the Picts, Saxons and Scoti continued their raids, which may have increased in scope. In 405 the Irish king Niall of the Nine Hostages is described as having raided along the southern coast of Britain.
Both the Eastern and Western Empires were suffering from incursions of large groups from Germanic tribes, whom the Romans referred to generically as "barbarians". In 406 a group of Alans and Goths led by Radagaisus invaded Italy. The group included women and children and is estimated to have been 90,000–100,000 strong, of whom more than 20,000 were fighting men. For six months they devastated northern Italy, capturing and sacking several cities. After concentrating his forces, Stilicho caught the Goths while they were besieging Florentia (modern Florence) and defeated them at the Battle of Faesulae; 12,000 prisoners joined the Roman army and so many captives were sold that the market in slaves collapsed. The Western Empire's problems with barbarian intruders were far from over, however.
Life Little is known of Constantine before he was declared emperor. His date and place of birth are unknown, as is his marital status. He had two sons, although their names prior to being given more regal-sounding ones are likewise unknown. Regarding his personal habits, one fifth-century historian described him as a glutton and another considered that his major flaw was being inconstant in his policies.
Rise In 406, the approximately 6,000 troops of the Roman field army based in Roman Britain were dissatisfied. They had not been paid for several years, a large contingent had left to fight on the continent four years earlier and had not returned, the coastal defences had been dismantled to form the new field army and their commander had been replaced. They revolted and determined to choose their own leader. Their first choice was a man named Marcus, whom they appointed emperor. After a short period, unhappy with his performance, they killed him and appointed Gratian. He also failed to meet the troops' expectations and was killed after four months. On 31 December 406 several tribes of barbarian invaders, including the Vandals, Sueves and Alans crossed the Rhine, perhaps near Mainz, and overran the Roman defensive works in a successful invasion of the Western Roman Empire. Hearing of the Germanic invasion the Roman military in Britain was desperate for some sense of security in a world that seemed to be rapidly falling apart. They next chose as their leader a man named after the famed emperor of the early fourth century, Constantine the Great, who had himself risen to power through a military coup in Britain. This Constantine was a common soldier, not an officer, and early in 407, possibly February, his fellows acclaimed him as emperor. The modern historian Francisco Sanz-Huesma differs and proposes that Constantine was a skilled politician who engineered the three acclamations with the (successful) intention of eventually raising himself to imperial power. Early coins of Constantine call him "Flavius Claudius Constantinus", a name he probably adopted because he thought it was that of Constantine the Great, when in fact it was that of his son, Constantine II. The style and legends of these early coins were also copied from those of Constantine II.
Rebellion in Roman Britain was not unusual, a contemporary described it as a "province rich in usurpers". It was on the periphery of the Empire and there was a common view that it was overlooked in terms of resources and patronage. Such revolts were usually short-lived; Constantine was uncommon in both establishing a lasting power base and in successfully exporting his rebellion to the mainland. Constantine moved quickly: he appointed two officers already in Gaul (modern France) as generals, Justinianus and Nebiogastes, instructing them to seize Arles and the passes which controlled traffic to and from Italy. He crossed the Channel at Bononia (modern Boulogne), taking with him all of the 6,000 or so mobile troops left in Britain and their commander, the general Gerontius. This denuded Roman Britain of front-line military protection and explains the disappearance of the legions in the early fifth century. Constantine travelled to Lyon, where he set up his headquarters and commenced minting coins in his own name. The Roman army in Gaul declared for him, followed by the civilian administration in Hispania (modern Spain and Portugal). The central Roman authorities did not respond to the Germanic invasion, and Constantine's forces got the better of at least one confrontation with the Vandals. Constantine also negotiated agreements with the Germanic groupings of the Franks, Alamanni and the Burgundians, thus securing the line of the Rhine. The main Vandal force and their allies moved into northern Gaul (modern Belgium).
The Western Roman emperor, Honorius, and his commander-in-chief Stilicho were in conflict with the Eastern Roman Empire and allied to a large force of Visigoths under Alaric. The relationship with the Visigoths was shakythey were demanding land or money for their services. An agreement was reached for a joint West Roman-Visigoth army to threaten the Eastern Empire to extort land from it which would then be given to the Visigoths. This manoeuvre was supposed to commence in May or June 407. By then the Vandals and their allies had broken into Gaul, where Constantine had control of the army and was claiming the imperial throne. Sending a large Western Roman force to the east would have left Italy open to invasion by one or both of these groups and so the offensive was cancelled. Instead a small army led by Sarus the Goth was sent west to put down Constantine's revolt while Stilicho's main army waited on events.
Sarus defeated the army commanded by Justinianus in a pitched battle, killing Justinianus. Constantine personally moved against Sarus, but was besieged in Valence. Nebiogastes attempted to negotiate and was killed by Sarus. Another army, led by Gerontius and Edobichus and largely made up of freshly recruited Franks and Almannics, arrived to relieve Valence after a week of siege. Sarus was forced to retreat into Italy. Central control had deteriorated to the extent that Sarus needed to buy his passage through the Alpine passes from the brigand Bagaudae, who controlled them. With this success Constantine established control over most of Gaul and the Alpine passes into Italy.
Co-emperor
By May 408 Constantine had captured Arles and made it his capital, taking over the existing imperial administration and officials, and appointing Apollinaris as chief minister (with the title of ). Heros was installed as a pliant archbishop of Arles in spite of local opposition. Constantine commenced minting large quantities of good quality coins at Arles, possibly using bullion seized from Sarus's loot during his hasty retreat, and made a show of being an equal of both the Western and Eastern Emperors.