An Excerpt from My Recent Treatment of the Name Lancelot

... Chretien de Troyes places Lancelot of the Lake at Glastonbury in place of Gildas in the story of Melwas' (= Meleagant) abduction of Guinevere. The tale had first been told in Caradog of Llancarfan’s “Life of Gildas”. I'd always wondered: why the substitution?

Well, I've always felt it was fairly safe to link Galahad, Lancelot's son, with Gildas. The preferred form of Galahad is Galaad. This is thought to be, transparently, from Galaad, the ancient Greek form of the biblical place name Gilead, often found in the Septuagint and apocryphal books like 1 Maccabees. And this is okay, so far as it goes. But we need to take it one step further - to the form Gilead, which is a close error for Gildas.

The famous Castle Corbenic of Galahad's use is not, as I once thought, Dinas Bran (see below), but the -carfan element of St. Cadog's Llancarfan (the letters b and f commonly substituting for each other; early MSS. actually have Carban spellings; see https://heneb.org.uk/archive/ggat/cadw/historic_landscape/llancarfan/english/llancarfan_001.htm). Gildas spent a considerable time at Llancarfan. The castle would be the large Castle Ditches hillfort next to the monastery. This is very near Campus/Palud Elleti, Chretien's Camelot, which was between Penmark and the River Thaw.

We may begin to look for the name Lancelot by noting that in French, -ot could act as a diminutive suffix used of objects or names. 

And to further muddy Lancelot of the Lake (pun intended!), the initial /L/ of Lancelot could have originally stood for L', the definite article "The."

Fortunately, in Old French, l'ancelot literally means "the servant" or "the squire." It derives from the root ancel, which traces back to the Late Latin ancilla (maidservant) and anculus (manservant).

From https://dmnes.org/name/Ancel:

France

Latin

● 2h12thC Ansellus (nom) NotSLdN III; 1093 Ansello (abl) CartStPC VI; 1135 Ansellus (nom) clairvaux-12thc 7; 1139 Ansello (abl) HAP p. 371, Ansellus (nom) ibid. p. 372; 1147 Ansello (abl) clairvaux-12thc 18; 1156 Anselli (gen) CartYonne1 CCCLXXXIII, Ansellus (nom) ibid. CCCLXXXIII; 1163 Anselli (gen) clairvaux-12thc 103, Ansellus (nom) ibid. 103; 1178 Ansello (abl) NotSLdN I; 1261 Ansellum (acc) ArrestReg-volI II, St. Martin; 1268 Ansellus (nom) NDParisII 2-V; 1269 Ansellus (nom) ibid. 2-III; 1273 Anselli (gen) ibid. 2-XLIII

◑ c1170 Ancelini (gen) CartNDdOurscamp LXXXIV; 1231 Anselinus (nom) NDParisII 2-CV; 1260 Anselinus (nom) ArrestReg-volI XXI, Ascension; 1378 Anceleti (gen) hanquetvol1 858

Old French

● 1292 Ansiau (obl) HistHdVParis p. 116; 1296 Anciau paris1296 p. 30, Ansiau (obl) HistHdVParis p. 131; 1313 Anseau Paris1313 p. 30

◑ 1303 Anselet (obl) ArchReimsII1 XL

Middle French

● 1392 Anceau MemBret-II col. 598; 1404 Anceau HistHdVParis no. 4

◑ 1404 Ancelot HistHdVParis no. 4; 1423 Ancelet favier 147

But if Lancelot = The Servant, how are we to connect that Gildas?

Simple. 

Although the etymology of the name Gildas is uncertain, it might easily have been associated with Irish gilla, Scottish giolla, "servant". In this way, 'The Servant"/Lancelot is simply a descriptor or title for Gildas himself.

A good scholarly discussion of this origin for the name Gildas may be found here:

https://dokumen.pub/the-legacy-of-gildas-constructions-of-authority-in-the-early-medieval-west-studies-in-celtic-history-43-9781783276721-9781787446816-9781800104723-178327672x.html

We might have in Gildas a form of the early-attested Gilla de, "Servant of God." We find this name in medieval texts and it is even assumed by the sea god Manannan mac Lir. 

https://www.academia.edu/110670059/The_Waves_of_Manannan

I would remind readers that Gildas was born in Arecluta, i.e. Clydeside. In Welsh Clyde is Clud, as in Alclud, the Rock of Clyde. There is another word in Welsh spelled clud:

GPC

clud 

[< *kloi-tā-, cf. Llad. clītellae or gwr. *klei- ‘gwyro, gogwyddo, pwyso’] 

eb. ll. cludau.

a Y weithred o gario neu gludo, dygiad; llwyth, baich, pwn, bwndel; celfi at daith, bagaets; cyfoeth, ysbail, anrhaith:

carriage, the action of carrying; load, burden, pack, bundle; luggage, baggage; wealth, booty.

This explains why when we first encounter Lancelot in Chretien de Troyes, he is riding in a cart. 

Thus Lancelot is not substituted for Gildas in the Melwas story. He is Gildas.

I suspect Lancelot, i.e. Gildas, is 'du Lac' 'of the Lake' because of the situation of his Glastonbury as described in his VITA:

"Glastonia, that is, the glassy city, which took its name from glass, is a city that had its name originally in the British tongue. It was besieged by the tyrant Arthur with a countless multitude on account of his wife Gwenhwyfar, whom the aforesaid wicked king had violated and carried off, and brought there for protection, owing to the asylum afforded by the invulnerable position due to the fortifications of thickets of reed, river, and marsh." 

It makes good poetic sense if Arthur's sword Caliburnus (in Geoffrey of Monmouth) is forged in Avalon(= Glastonbury), and that Arthur's Lady of the Lake sword should come from and be returned to the Glastonbury marshes.