When archaeologists open Viking warrior graves in Scandinavia, they keep finding swords signed with a Frankish name: Ulfberht. Roughly 170 of these blades survive from the ninth to eleventh centuries, and this episode uses their metallurgy and find locations to reconstruct a medieval arms trade, an arms embargo, and a black market. We start with the weapon itself, a light 1.2-kilogram one-handed blade with a forge-welded inlaid signature.

We compare pattern welding, the composite technique European smiths used to stretch scarce steel, with the hyper-eutectoid crucible steel found in later Ulfberht blades, material that could not be made in Europe and likely traveled from Central Asia along the Volga trade routes. Then we ask why swords made in the Rhineland turn up mostly in Norway, Sweden, and Finland, and what misspelled signatures reveal ...