The Charm of Making spoken by Merlin & Morgana is an attempt at Old Irish that translates to: "Serpent's breath, charm of death and life, thy omen of making." The phonetic rendering, as spoken in the movie, is: /ana:l nathrakh, u:rth va:s bethud, dokhje:l djenve:/. In Irish, the phrase is: 'An?il nathrach, ortha bh?is bheatha, do thuar dhéanamh', which is pronounced similarly but not exactly as in the movie.
The initial fight scene in the movie had to be filmed three times. It was filmed at night and the first two times, all the film came out underexposed due to a fault in the exposure meter. The cameraman had a nervous breakdown over the issue and quit.
The fight between Arthur and Lancelot was filmed on the Powerscourt estate. The battle scenes in Laurence Olivier's film version of Henry V were also filmed there due to wartime restrictions in England.
The names of the 25 knights inscribed on the Winchester Round Table are given as: Galahad, Lancelot du Lac, Gawain, Percivale, Lionell, Bors de Ganis, Kay, Tristram de Lyones, Gareth, Bedivere, Bleoberis, La Cote Male Taile, Lucan, Palomedes, Lamorak, Safer, Pelleas, Hector de Maris, Dagonet, Degore, Brunor le Noir, Le Bel Desconneu, Alymere, and Mordred.
Before the final battle, Arthur's knights are camped around a "Stonehenge" like formation on a hill. The rocks were fake and part of the set. According to John Boorman, some American tourists were driving by down below and saw the formation. Thinking they were real, the tourists hiked up the hill, and Boorman had to explain to them that they were not real but part of a movie set.
All of the armor used in the film was hand made out of aluminum, primarily by British armorer Terry English. English custom-fit the suits of armor for the principal characters, but kept the overall style the same for members of different groups, especially prominent in the nearly "uniform" armor of the Knights of the Round Table. English can be seen in the film during the tourney scenes; he is the blacksmith who looks up at Arthur (Nigel Terry) when the future king is chasing a thief and stops to contemplate filching a sword from the armorers' tent.