Other mistake: When King Arthur confronts Mordred in the Abbey ruins on the cliff tops, you can see two fighter jet planes flying up the coastline behind him.
Knights of the Round Table (1953)
1 other mistake - chronological order
Directed by: Richard Thorpe
Starring: Robert Taylor, Ava Gardner, Mel Ferrer, Anne Crawford
Revealing mistake: In the scene where Lancelot runs into and fights Arthur's ambushers, he runs one of them through with his sword. It is visible that he stabs his opponent past the body, but close enough for the appearance.
Trivia: Anne Crawford plays Morgan Le Fey, the mother of Modred (Stanley Baker). In real life, Crawford was only eight years older than Baker.