Arthur Rackham's Illustration of Mordred and Arthur at Camlann
I long ago successfully etymologized the name Medraut as deriving from Latin/Roman Moderatus. Years ago Professor Oliver Padel agreed with me on this and others have since fallen into line. But I did not pursue the matter further - until now.
Here is the definition of moderatus from the online Perseus dictionary:
moderātus adj. with comp. and sup.
P. of moderor, within bounds, observing moderation, moderate : senes: Catone moderatior: consul moderatissimus: cupidine victoriae haud moderatus animus, S.—Plur m . as subst: cupidos moderatis anteferre.— Within bounds, moderate, modest, restrained : oratio: convivium: doctrina: ventus, O.: amor, O.: parum moderatum guttur, O.
The reader will note 'modest' is one meaning assigned to this word.
I will now turn to the pages of Gildas, where we are told Ambrosius Aurelianus was a 'viro modesto', a MODEST man.
For the sake of comparison, here is the same dictionary's definition for modestus:
modestus adj. with comp. and sup.
modus, keeping due measure, moderate, modest, gentle, forbearing, temperate, sober, discreet : sermo, S.: adulescentis modestissimi pudor: plebs modestissima: epistula modestior: voltus, T.: verba, O.: mulier, modest , T.: modestissimi mores: voltus modesto sanguine fervens, Iu.—As subst: modestus Occupat obscuri speciem, the reserved man passes for gloomy , H.
Both Latin modestus and moderatus are found the Indo-European root med-,'to measure, to allot, to mete out':
3. Suffixed form *med-es-.
a. modest; immodest from Latin modestus, "keeping to the appropriate measure" moderate;
b. moderate; immoderate from Latin moderārī, "to keep within measure" to moderate, control. Both a and b from Latin *modes-, replacing *medes- by influence of modus
Thus the words modestus and moderatus are consonant in meaning.
Ambrosius (the 'divine/immortal one'), before he was wrongly identified with Lleu/Mabon of Gwynedd (and later still with Myrddin of the North), was said to have fought a battle at Wallop in Hampshire. This is not too far north of the battle sites ascribed to Arthur/Cerdic/Ceredig son of Cunedda. In addition, the Camlann sites in NW Wales are in Gwynedd.
While it may seem a stretch to identify Medraut/Moderatus with the viro modesto who was Ambrosius, it is possible that by the time Arthur had come to the forefront as the chief hero of the Welsh in the work of the 9th century Nennius, someone had found it necessary to "disguise" the fact that the latter had died fighting the former champion of the Britons, the 'last of the Romans.' Alternatively, the 'viro modesto' of Gildas may have been a simple substitution for Moderatus, this last having been mistaken for an adjective rather than a proper name.
We must also remember that the earliest reference to the deaths of Arthur and Medraut - that of the Welsh Annals - does not tell us whether these two chieftains were fighting together against a common foe or against each other. Chronological problems also occur, especially if we accept my earlier identification of Ambrosius Aurelianus with the 4th century Gaulish governor of that name. Most Arthurian scholars prefer to see in A.A. someone of the 5th century who had been named after the governor or who was somehow related to him. I've shown in the past that St. Ambrose, son of the governor, also became confused in some respects with the military leader A.A.
We can only say this much if A.A. really was 'Medraut': the Camboglanna Roman fort at the west end of Hadrian's Wall is out of the running as Arthur's Camlann. As Arthur was Ceredig of Ceredigion, and Ceredigion bordered on the Camlanns in Gwynedd, and as A.A. became in legend the Lord of Gywnedd (= Lleu/Mabon), the only good candidates for Camlann are those in NW Wales.
A last possibility has only recently occurred to me: that the ruler at Dinas Emrys was originally called Moderatus, and that this name became confused with that of the modest man A.A. In Welsh tradition (whether due to Geoffrey of Monmouth or not!), Medraut was the son of Lleu - the very god who was anciently claimed as Lord of Gwynedd. So we may have a chieftain named Medraut whose main citadel was Dinas Emrys, and who claimed descent from the god Lleu. This chieftain fought at the Camlann which lay between his kingdom and that of Ceredigion and at that battle he and Arthur/Ceredig both fell.
I realize that I've now made the identity of A.A. even murkier. But I may have at least shed a little more light on who Medraut really was.
In conclusion, I acknowledge the fact that this idea is not very convincing. Suffice it to say it is an interesting coincidence.