In retaliation, Lucius gathers heathen armies from Spain and North Africa and invades the lands of Arthur's allies on the continent in Brittany.
He is also mentioned as married to daughter of one of his pagan allies, a Middle Eastern ruler named only just as the Emir (Amiraut), in the poem Didot Perceval.
In the Historia, the war begins when Lucius' nephew (uncle in the Alliterative Morte Arthure), Gaius Quintilianus, is killed by Gawain after he insults the Britons.
Lucius himself then dies by unknown hand as the armies of Rome and the Empire's Germanic allies are conquered by Arthur's forces.
The figure of Lucius is clearly fictional, though whether Geoffrey took the character from tradition or completely created him for propagandist purposes is unknown, as is the case with much material in his Historia.