The Damascus sword is the sharpest sword in the world. These swords were commonly used by Crusaders in the 17th century and contained carbon nanotubes.
According to legend, Damascus swords were sharp enough to slice a piece of silk in half and cut through rock, metal and other swords. The sharpness is due to the molecular structure, which scientists have studied to find that the softer steel blade is made of hard carbon nanotubes forming nanowires, which are extremely strong. Some of the nanowires are made of cementite, a resilient, iron-based mineral. Damascus swords are thought to be so strong because the hard nanowire layers are coupled with softer steel, called wootz, to create a strong, flexible blade.