Honorius was the second son of Theodosius the Great and Aelia Flavia Flaccilla and was born in AD 383.
In AD 393 he was raised to be co-Augustus at Constantinople.
At Theodosius' death in AD 395, Honorius assumed the role of emperor of the west, with his brother Arcadius becoming emperor of the east.
This division of the empire into eastern and western parts was the decisive one, which sent the two on separate ways. Had the empire effectively been split by Valentinian, it had still functioned as a unit. One of the two emperors had always enjoyed seniority over the other. However, the accession of Arcadius and Honorius is widely seen as the division of the Roman empire into two completely separate parts.
Arcadius is therefore often quoted as the first 'Byzantine' ruler.
At his accession Honorius was only twelve years old and Theodosius had appointed a guardian to watch over matters of state for him, - the 'Master of Soldiers' Flavius Stilicho.
Stilicho was half Vandal, half Roman, and married to the emperor's cousin Serena. The daughter of this couple, Maria, was even married to the young Honorius in AD 395.
Theodosius had chosen well in Stilicho, for he was a man of considerable ability.
Though Stilicho's regency was marred by a bad relationship with Constantinople which eventually degenerated into open hostility.
For one, Stilicho made claim that Theodosius had granted him guardianship over both emperors. A statement which may well have been true.
But the power behind the throne in Constantinople was the praetorian prefect Flavius Rufinus who had no intention on surrendering his power to the Vandal Stilicho.
Furthermore, Stilicho chose to attempt to add the Balkan territories of praefecture of Illyricum to the western empire and so at least enlarge western power.
Blatantly pursuing this goal he marched his troops into Greece at the outbreak of the Visigoth rebellion against Arcadius under the pretext of seeking to help the eastern empire.
But when ordered out of the eastern territories by Rufinus in Constantinople, Stilicho backed down and withdrew, leaving behind a few legions under the command of his Gothic general Gainas, which were to to be restored to the east.
As they had marched to Constantinople, they stabbed Rufinus to death as he came to welcome them. Clearly this assassination was the work of Stilicho and it did irreparable damage to the relationship between the eastern and the western empire.
But with the Visigoths still rampaging through the Balkans and Greece, Stilicho was in AD 397 formally asked by Constantinople, now governed by the eunuch Eutropius, to come and aid them against the barbarians.
As Stilicho moved into Greece, but Alaric and his Visigoths got away. Constantinople, forced to buy Alaric off by making him 'Master of Soldiers' in the Balkans, responded furiously by pronouncing Stilicho a public enemy. It had since been the cause of much speculation if Stilicho indeed did let his fellow German Alaric get away, or if indeed Alaric simply outwitted his foe.
In the very same year, AD 397, an uprising in Africa took place, led by the military commander called Gildo.
Gildo revolted against the western empire, of which his territory was a part and declared for Arcadius instead.
This though meant that the valuable African grain supply to Rome fell into the hands of the east.
Stilicho of course suspected the doings of Eutropius in this, though he did not follow the manyfold advice of starting an open war with the east. Instead he engaged in systematic diplomatic intrigue which eventually, in AD 399, saw Eutropius discredited, thrown from office and banished into exile.
Meanwhile Stilicho crushed the rebellion of Gildo and returned Africa to the western empire.
The hostilities of the Visigoths in the Balkans eventually were deflected from Constantinople toward the west by Eudoxia, Arcadius' wife and effective regent of the east.
In AD 403 Italy was terrified by an invasion of the Visigoths, smashing their way into the very homeland of the empire. But Stilicho, gathering troops from the Rhine, Britain, and from wherever else he could, managed to halt their advance and force them back out of Italy.
Meanwhile Honorius decided to move his residence from Mediolanum (Milan) to the greater safety of Ravenna in AD 404.
And Italy was indeed far from safe. In AD 405 the Ostrogoths, who had in previous years been gradually forcing their way across the Middle Danube, now under the leadership of Radagaisus flooded over the Alps into Italy.
But once again Stilicho saved the day, by decisively defeating them at Faesulae (Fiesole).
Stilicho now made plans to attack the eastern empire. But he was forced to abandon them as in AD 406 huge numbers of Vandals, Suevi (Sueves), Alemanni, Alans and Burgundians crossed the frozen Rhine.
Moguntiacum (Mainz) and Treviri (Trier) fell to the invaders who then spread out into Gaul in a wave of utter destruction.
As Stilicho struggled to stem the tide, the troops of Britain mutinied in AD 406, seeing a series of men pronounced emperor and killed until eventually Constantine III achieved rule over the island. Parts of Gaul and Spain soon joined him.
In such desperate times, Stilicho saw no other means to save the empire as to buy off Alaric and his Visigoths. The price demanded was four thousand pounds of gold. The senate was unwilling to yield such a obscene amount of money, but Stilicho forced them to comply.
But the pressure brought to bear on the senate should cost Stilicho dear. The senators resented his methods and conspired to rid themselves of him. Soon after Stilicho was accused of plotting with Alaric to depose Honorius and instead make his own son Eucherius emperor of the west.
The troops at Ticinum (Pavia) were persuaded to stage a mutiny against their leader and in AD 408 Stilicho surrendered at Ravenna to the emperor and was executed.
The effect of Stilicho's downfall was disastrous. Stilicho's many German soldiers thereafter all went over to Alaric in order to avoid persecution by the Romans.
Alaric himself, no longer hoping for the bribes to keep the peace he'd received from Stilicho, now marched on Italy. Rome was only rescued by payment of another vast payment by a reluctant Honorius.
For a short period Alaric and Honorius, strangely co-existed in Italy. Occupying Portus Augusti, Alaric in AD 409 even set up a puppet emperor of his own, the prefect Priscus Attalus, who was confirmed by the Roman senate, terrified at having the barbarians so close to their capital.
But Attalus didn't last for long, soon being deposed again in AD 410 by Alaric.
Then, in AD 410, Alaric's camp was attacked by Sarus, another Visigoth leader. Did Alaric know Sarus as an enemy of his, he believed this attack to have been done on Honorius' behalf.
Alaric broke off all negotiations with Honorius and marched on Rome. Agents within the city opened the gates and on 24 August AD 410 the Visigoths fell upon Rome and sacked the ancient city for three days.
Thereafter Alaric, taking with him the emperor's twenty year-old half-sister Aelia Galla Placidia, moved on into the south of Italy. Apparently he had plans to embark and conquer Africa. But before any of this plan could be put into action, Alaric died at Consentia (AD 410).
In AD 411 the able commander Constantius (who was to become Constantius III in AD 421) became Honorius' leading military commander, in effect filling the vacancy left by Stilicho.
While the Visigoths, now led by Alaric's brother-in-law Athaulf, was still lingering in Italy, the empire of the break away emperor Constantine III was collapsing. It extended from Britain to northern Spain. It broke down, partly owing to the revolt of one of his officers in Spain, Gerontius, and partly because of the military talent of Constantius. Gerontius was besieging Constantine III at Arelate (Arles), when Constantius intervened decisively.
Gerontius retreated to Spain, where he was murdered, Constantius captured Arelate and with it Constantine III, who was executed.
Returning to Italy, Constantius effectively drove the Visigoths out into Gaul in AD 412.
Meanwhile though a new usurper, Jovinus, was proclaimed emperor in Gaul.
Yet another complication arose when in early AD 413 Heraclianus, Count of Africa, proclaimed himself emperor, too. Worse still, Heraclianus, having already amassed a great fleet, sailed for Italy.
Though Heraclian's rebellion proved an utter fiasco. He was captured and executed in midsummer. But meanwhile it had not been possible for Constantius and Honorius to take direct action in Gaul. Instead they had had to bargain with Athaulf, who then crushed Jovinus. Also the Burgundians, who were the allies of Jovinus, proved too powerful to deal with. And so they were granted the right to form their own kingdom within the empire ad henceforth were considered federates (foederati) who would act as allies to the emperor.
All along Aelia Galla Placidia, Honorius' half-sister had remained in the hands of the Visigoths ever since the sack of Rome.
However, the princess had in Constantius a devoted admirer, who wanted her back. Naturally emperor Honorius also understood it a stain on his honour that his sister should be a hostage of the barbarians.
It was part of the bargain with Athaulf that Galla Placidia should be returned. But the Roman part of the bargain, the supply of corn to Athaulf's troops, had been come to nothing due to the rebellion of Heraclian. Consequently Athaulf, instead of returning the princess, married her himself in AD 414 at Narbo (Narbonne), apparently with her own willing consent, - but without that of her brother.
The marriage failed to draw Athaulf any closer to the imperial court, in fact he set up Priscus Attalus as his puppet emperor of the west in Gaul.
This was a step to far for Constantius who now marched into Gaul and forced Athaulf to withdraw into Spain. Meanwhile Priscus Attalus was captured and taken back to Rome.
Once in Spain and left to his own devices Athaulf set out to conquer Spain. But there he was murdered in AD 415, and his successor Wallia struck a bargain with Rome.
Wallia agreed to hand Galla Placidia back to the Romans (where she reluctantly accepted the hand of Constantius) and to make war with the other barbarians in Spain.
Faced by the dual threat of Romans and Visigoths, the other barbarians in Spain (Vandals, Alans and Sueves) hastened to seek peace with the empire, which they obtained.
In exchange the Visigoths were allowed to return to Gaul, setting up their capital in Tolosa (Toulouse). The agreement between Wallia and Honorius was similar to the treaty made by Theodosius with the Visigoths in the Balkans almost thirty years earlier (AD 382), or with the Burgundians more recently in the west.
It defined the Visigoths as federates within the empire. They enjoyed self-rule over their territory in Aquitania, though they needed to provide troops to the empire.
Having rescued the western empire from utter destruction, Constantius was rewarded by being made co-Augustus in AD 421 and his wife Galla Placidia was invested as Augusta.
Though the eastern emperor, Theodosius II, refused to accept either the elevation of Constantius III or of Placidia, which led to threats of war by Constantius III and a renewed deterioration of relations between east and west.
But after a reign of only seven months Constantius III died.
After his death, Honorius, who had always been very affectionate toward his (half-) sister began making advances towards his Galla Placidia, caressing her and embracing her in public. Not merely did this cause public outrage but it alienated her from him and she fled to Constantinople in AD 423, taking the two sons of Constantius III with her.
In the same year, AD 423, Honorius fell ill and died.