Caliburn

History
Caliburn was a sword produced in Avalon by Vivian as a gift to Merlin. Merlin decided to use its magic to put it in a rock and later give it to the student of his that he would decide to become king. Eventually Merlin decided on Arthur, teaching him swordplay and how to be a knight, and Arthur pulled it from the stone, becoming King of Britain. It quickly showed its power by casually cutting down 200 traitors to the country. Arthur used it as his primary weapon until his war with all the other countries, where it was broken in a training session with Lancelot.

Power
Caliburn is an extremely powerful sword, built in Avalon itself, though its power pales greatly in comparison to Excalibur. Still, Caliburn's full power was enough to draw out Lancelot's full power, something that no other entity in the time of the Round Table was able to do. It was still, however, not powerful enough to survive clashing with Lancelot's full power.