Excalibur. Arthur's sword, symbol of divine kingship, is as much a character in the legend as any human or supernatural being. Excalibur is a symbol of the responsibility of power.
It was also said to be unbreakable and extremely sharp through magical enforcement (Day 28, Peterson 52). Especially in older tales, Excalibur shines and blazes when it is drawn or used, "When Arthur drew it from the scabbard, it 'cast a great light as if two torches had been kindled there'," (Loomis 422).