Magnus Maximus was born to a poor Spanish family, probably in the province of Callaecia in north western Spain.
After a military career, Maximus came to serve under Theodosius the Elder in Britain in AD 369, and in Africa from AD 373 to 375.
His efforts were rewarded by being granted overall military command in Britain, where he successfully campaigned against the Picts and Scots.
But the army was very disillusioned and dissatisfied with its emperor Gratian. In particular jealousies toward privileges awarded to barbarian units fighting for the empire ignited much ill-feeling with the soldiery.
Finally, in AD 383 it all boiled over and the garrison in Britain revolted and proclaimed Maximus as the new Augustus of the west.
At once the new emperor crossed the Channel with his troops, taking Gratian by complete surprise.
As Gratian marched his troops west to meet the usurper at Lutetia in battle, his troops simply deserted him and changed allegiance to Maximus.
Gratian fled, but was caught up with by Maximus' 'Master of Horse' Andragathius who assassinated him.
Maximus now established his capital at Treviri and began negotiations with Theodosius, emperor of the east, who reluctantly recognized him as emperor, if only to save young Valentinian II who still remained in charge of Italy, Pannoniae and Africa.
With his recognition as emperor, Maximus adopted the name Flavius, in order to portray himself as an adopted member of the imperial family.
Maximus was a orthodox Catholic who, like Theodosius in the east, vehemently pursued and punished heretics and pagans.
In AD 387 Maximus elevated his infant son Flavius Victor to be co-Augustus.
Then, in the summer of AD 387, Maximus invaded Italy in a successful attempt to oust Valentinian II. The young emperor Valentinian II fled with his mother to Theodosius in Constantinople.
But Maximus attempt on increasing his realm of influence backfired. Theodosius was no longer tied up in trouble in the east anymore and stood ready to launch an attack on the usurper.
In AD 388, with Maximus staying behind in Aquileia, Andragathius led his army against Theodosius, only to be defeated at Siscia.
Thereafter his brother Marcellinus led the re-grouped army back into battle, but he too was defeated at Poetovio.
Maximus was captured and pleaded for the victor to show mercy. Though Theodosius showed none and had him executed (AD 388).
His son, Flavius Victor, was captured by Arbogast, Theodosius 'Master of Soldiers', and was also put to death.