Continuity mistake: Morgana becomes old after she recites "The Charm of Making". They use another older actress to portray her and she's wearing the same costume and head dress but they neglected to put on the long dangling earrings that she was wearing in the previous shots when she was younger. (02:07:00)
Continuity mistake: When Arthur is dying after killing Mordred, he drops to his knees with the spear still through him. When Sir Percivle is next to him getting his last instructions, the spear is gone.
Continuity mistake: After speaking to Arthur, Mordred catches up to and kills Uryens by the lake with his spear. The close-up of the spear in Uryens' back shows beads dangling about one foot from the tip. In the long shot of his body we see a different spear with no beads at all, just a short dangling piece of rope. (01:48:45)
Continuity mistake: Several knights joust and the winner has the right to try to pull Excalibur out of the stone. The winner tries but cannot do it and sets the sword rocking back and forth in the stone. The shot lasts until Excalibur stops moving, then in the next shot it's wobbling back and fourth again. (00:26:00)
Continuity mistake: At the beginning of the movie Merlin says, "Show the sword" and we see Excalibur for the first time in a human hand. Uther at first holds the sword with his thumb wrapped around the handle, then in the close-up his thumb is pointing upward then in the next shot his thumb is wrapped around the handle again. (00:03:55)