The second candidate is a Romain; Aurelius Ambrosius. He is mentioned in Gildas' Britons History as the leader of an army. He tells that the Britons obtain a victory under the leadership of Ambrosius Aurelius.

Ambrosius Aurelianus is known in the Welsh history as Emrys Wledig. He was the eldest son of Constantine the Blessed. Gildas described Ambrosius as the last of the Romans and the chief protagonist against the Saxons.

The story of Gildas shows that he had a high regard for Ambrosius, because Ambrosius was the only one who wasn't criticized by Gildas. Instead Gildas referred to him as “a man of unassuming character, who alone of the Roman race chanced to survive the shock of such a storm as his parents, people undoubtedly clad in the purple, had been killed in it, whose offspring in our days have greatly degenerated for their ancestral nobleness.1

In Historia Brittonum , written by Nenius, Ambrosius appears as the boy who tells Vortigern about the dragons. Geoffrey changed his name into Merlin and makes a king of Ambrosius, just like Geoffrey added and changed many more characters.

However, when we look at the data in which Ambrosius lived, he was way too old to have fought the battles we assume Arthur did. He was probably in his 70s at least when he should have fought at Camlan. The average life expectancy in the Dark Ages was around 40. It wasn't possible that Ambrosius was alive during the time of Arthur. He can't even have been a famous soldier at that time2.

So Ambrosius isn't the real Arthur, but probably some battles of Ambrosius have been mixed up with the Arthurian legend. This makes Ambrosius a small historical base for King Arthur.