The Sword of Caliber was an Astral artifact created by the Lady of the Loch to assist Weasel in completing the Prophecy of Two. Not only was the sword nearly indestructible (especially after Rhys's first death), it also had a power that allowed it to absorb the power of anything it came into contact with it. It also became a Shadow artifact once it absorbed the Horned Crown on Arturia.
List of things absorbed by the Sword of Caliber
1. Inquisitor Rhys's armor
2. Skathi's Stinger
3. The Lamp of Luxury
4. The Horned Crown
5. The Eye of Horus
6. The Jersey Devil