The concept of the "most powerful" sword is subjective and can be interpreted in different ways, depending on the criteria used to define power. Several swords throughout history are often associated with power, whether in terms of their historical significance, cutting ability, or cultural impact. Here are a few swords that are often considered powerful:

1. Excalibur: Excalibur is the legendary sword associated with King Arthur, the mythical British monarch. It is said to possess magical properties and represents Arthur's rightful claim to the throne. Excalibur symbolizes power, leadership, and the ability to unite and inspire.
2. Zulfiqar: Zulfiqar is a legendary sword associated with Islamic history and the Prophet Muhammad. It is a symbol of authority and strength, often depicted as a bifurcated or forked blade. Zulfiqar represents spiritual and temporal power and is considered a sacred artifact.
3. Durendal: Durendal is the mythical sword of Roland, a legendary knight from the medieval epic poem "The Song of Roland." It is said to possess incredible strength and invincibility. Durendal embodies courage, heroism, and the power to withstand adversity.
4. Joyeuse: Joyeuse is the legendary sword associated with Charlemagne, the medieval King of the Franks. It is considered a symbol of royal power and authority. According to legend, Joyeuse possessed mystical properties and was believed to contain the Lance of Longinus, which pierced the side of Jesus Christ.

It's important to note that the power of a sword can be attributed to various factors, including its historical significance, cultural symbolism, and the stories and legends associated with it. The perception of power can also vary based on individual perspectives, cultural context, and the symbolism attached to different swords.