In all this world, you cannot trust gods nor men, nor women or beasts. In your sword alone can you trust. But ever remember that a sword is not strength, Strength is the hand that holds it. Since ancient times, the bladesmith's dilemma has been how to produce a weapon that was both flexible enough to survive the impacts of combat, but at the same time hard enough to retain a keen cutting edge. Until modern times, the smith had basically only two ferrous metals to work with, wrought iron and carbon steel.
Wrought iron is very flexible, bends easily, but is too soft to hold an edge.
Carbon steel, on the other, hand can be made quite rigid and hard enough to stay a razor sharp. Unfortunately it is then also extremely brittle, so much so that any sudden blow will shatter it. The most sophisticated solution to this problem, developed during the early middle ages, was the creation of layered steels. In simple terms, this process involves stacking up alternating plates of iron and steel. The pile is then welded under the hammer into a single solid block.