12. Damascus Steel
Any time you see a knife or blade that is advertised as Damascus steel, here's a hint: it isn't. It's just wavy. Damascus steel is a methodology of crafting that has been lost to the mists of time, and produced the strongest, sharpest, and most flexible swords in the medieval age. Used in the Middle East from 300BC to 1700AD, the technique harnessed some of the inherent impurities in the special Wootz steel from India and Sri Lanka. We think that there were impurities of tungsten or vanadium that were needed to make the forging happen, as well as very specific controls of the thermal cycling during the creation. Swords made through this method have been analyzed and found to have carbon nanotubes throughout the length, which helps explain the incredible strength and flexibility.