In the movie, "Excalibur" a lot of magical incidents took place, mostly done by Merlin. If not for Merlin, Arthur wouldn't had ever been alive. Merlin is the one that conjoured up "the dragons breath" which allowed Uther to change his own identity in order to have sex with Tintagil's wife , and thus Arthur was born. Excalibur, Uther's sword, was created solely by some sort of magical forces. Merlin uses his magic through out the entire movie. Merlin would never use his magic against his own king, only for the purpose of helping him. Even when Merlin was tricked and then frozen, he was still able to use his magic to become a dream and help Arthur win his battle against Mordred. Just to prove Merlin's intelligence, he used his own mind to trick Morgana into using all of her magic and created the fog which later was used to defeat her own son.
The main source or power in "Excalibur" was indeed Excalibur itself. The king wasn't very strong without this special sword which aided him much throughout his rein. With first being King Uther's and then stuck in a stone upon his death for only his blood to take out, then it became Arthur's. With out Excalibur there was no real power or sense of togetherness within the land. When Uther first received the sword the kingdom was under control. When he was killed and he stuck the sword in the stone, there wasn't a king for many years and there was also no control or central power in the land. When Arthur pulled the sword from the stone and became