apparently the Vikings got the steel for their swords from as far away as Central Asia and India. and that steel was critical to the superior performance of those blades.
The famed Ulfberht sword is believed to have used steel forged in northern Iran, and transported through the Volga trade route (that followed the Volga river into the Caspian sea):
Something that is also mentioned in Neal Stephenson's Baroque Cycle. Which someone already mentioned in reference to gold. In really is an amazing dive into history, even if it's not 100% accurate.
https://en.wikipedia.org/wiki/Viking_sword
https://en.wikipedia.org/wiki/Crucible_steel