A companion of Arthur.
Lucius Artorius Castus
A commander in the Roman army, and suggested to be one of the potential historical basis for King Arthur. He had a long military career and one of his assignments were in York, Britain from c. 122 AD.
Batradz | The Legend of King Arthur
Sarmatians | The Legend of King Arthur
In Geoffrey of Monmouth, one of the Roman senators who became a war leader in Luciusís campaign against Arthur. He led a force of soldiers at the Battle of Soissons. Layamon split him into two characters: Lucas and Catellus.
Lucius the Glorius
He is highly praised by the chroniclers for converting the island to Christianity - a feat which, according to the Vulgate Estoire del Saint Graal, was prompted by Peter, a relative of Joseph of Arimathea, who arrived in Britain during Luciusís reign. Peter befriended Lucius and became his vassal after the latterís conversion. Lucius asked Pope Eleutherius to send Christian bishops to Britain. Under his reign, parishes and dioceses were set up in London, York, and Caerleon, and the old heathen temples were demolished. Those who refused to convert were destroyed.
When he died, however, he left no heir, and the Britons and Romans fought over who should be crowned in Luciusís place. The fighting lasted for several generations and resulted in a series of impotent kings before the kingdom was settled briefly under Asclepiodotus. According to Nennius, Lucius received his Baptism in 167, but Geoffrey says that he died in 156, and Layamon places his death in 160. Interestingly, the confused fourteenth-century Short Metrical Chronicle places his reign after Arthurís.
Luces, Lucies, Lucidar, Lucyus
The Roman Emperor whose empire Arthur attacked. Lucius summoned Arthur to Rome but was defeated. Geoffrey is rather vague as to his actual status and calls him procurator (governor); he implies he was inferior to the Emperor Leo of Constantinople. Wace and Malory both style him emperor.
Emperor Lucius, which was called at that time, Dictator of Procuror of the Public Weal of Rome,
sent twelve ancient, venerable ambassadors to Arthur's court to command from him the traditional obeisance and truage paid by the kings of Britain to Rome, and threatening dire war against Arthur if he refused to pay. Arthur refused to pay, citing the examples of
Belinus and Brenius, kings of Britain, [who] have had the empire in their hands many days, and also Constantine the son of Heleine.
This gave the king and his knights an excuse to play with weapons again after a long calm period. Arthur then crossed the Channel to meet Lucius on the Continent, perhaps reasoning that thus he could keep the destruction of warfare out of Britain. Lucius summoned Rome's allies to his aid, gathered his army and his personal bodyguard of "fifty giants which had been engendered of fields", and set out to meet Arthur in France.
Arthur sent Gawaine, Bors, Lionel, and Bedivere in embassy to command Lucius to return to Rome. Haughty words passed on both sides, Lucius showing himself as proud as Arthur, and finally Gawaine fell into a rage and slew Lucius' cousin Sir Gainus in the Emperor's presence.
The ensuing skirmish turned into a battle, with much bloodshed and taking of Roman prisoners. Lucius arranged an ambush to rescue the Roman prisoners as they were being sent to Paris. The attempt was foiled by Lancelot and Cador. A senator who escaped from the fray reached Lucius with this counsel:
Sir emperor, I advise thee for to withdraw thee; what dost thou here? ... for this day one of Arthur's knights was worth in the battle an hundred of ours. Fie on thee, said Lucius, thou speakest cowardly; for thy words grieve me more than all the loss that I had this day.
Lucius proceeded to the crucial battle with Arthur and met death from Arthur's own sword (he split Lucius' head in two with his sword Excalibur), following which Arthur marched on Rome, took it, and was crowned Emperor of Rome by the Pope himself.
It seems that Arthur was not able to maintain himself as both King of Britain and Emperor of Rome, for the Romans attacked him again when he was besieging Lancelot in France toward the end of his reign. We may perhaps surmise that there was originally but one campaign against Rome (in some medieval versions, Mordred makes his bid for the throne while Arthur is absent on the Roman campaign rather than while Arthur is in France for the specific purpose of fighting Lancelot).
It also makes sense, however, to accept a successful British war against Rome, as described by Malory, during the early or middle years of Arthur's reign, followed by a revolt of Rome against Arthur in the last, troubled years of his reign, as described in Vulgate VI.
It's uncertain whether it was Lucius or his predecessor who married Avenable.