Ulfberht is a name given to unique Viking swords used in Scandinavia around 800–1000 AD. The unique, high-quality steel they incorporated remained unparalleled until the Industrial Revolution. 171 such swords have been found so far, but only a few of these have been proven to be authentic Ulfberht swords. The earliest Ulfberhts date from circa 850. Little information is available about the fabrication of the Ulfberht sword. However, modern tests reveal that genuine Ulfberht swords were forged from crucible steel sourced from India. Crucible steel (of which Damascus steel is a type) has several advantages over the wrought iron more commonly used medieval weapons. Wrought iron is made of smelted iron ore, which is heated and forged to reduce iron oxide, remove slag, and increase carbon content by absorption through the exposed surface. The resulting weapon contains relatively little carbon (compared to crucible steel) and contains residual slag particulates that can significantly reduce the weapon's resistance to breakage. Crucible steel, conversely, goes through a liquid phase and results in a higher level of carbon as well as removing (or dissolving) all particulate impurities. This made the weapon intrinsically stronger. In addition to being more resistant to breakage, it would have allowed the smith to temper the weapon to a harder edge or to forge a thinner, more flexible blade without undue sacrifice of reliability. The technology was likely acquired by Vikings who traveled to Central Asia. Using speculative techniques, modern-day blacksmith Richard Furrer made a replica of an Ulfberht. The Ulfberht gave those who wielded it a significant advantage and was probably carried only by elite warriors and chieftains. Although of similar size and shape to a common Viking sword, the Ulfberht was far more durable and penetrated armor more easily. The characteristic identifying mark is the metallic inlay "+VLFBERH+T" on the flat of the blade close to the hilt. (The variation "+VLFBERHT+" was inlaid in swords made from lower-quality steel.) The sword's primary purpose was to break through an enemy's shield and mail armor; an Ulfberht's blade was very flexible compared to other weapons of the time and would not break or hang up as easily when penetrating wood or steel, thus giving the swordsman opportunity to move on quickly after cutting down a foe. "Ulfberht" is a Frankish word whose meaning is not known. The inscription "+VLFBERH+T" used Latin letters. The most common hypotheses are that it was the name of a swordsmith who passed his craft on to apprentices or family members, that it was the name of a group of craftsmen. The word is possibly a compound of the elements Ulfr 'wolf' (old Norse) and beraht 'light, bright, shining' (old high German, old Saxon). There are several variant spellings on the Ulfberht swords, of the more than 166 found by archeologists. Dr. Alan Williams (an archaeometallurgist who works at The Wallace Collection, a national museum in London.) has looked at 44 Ulfberht swords, and made a key discovery in the metallurgical composition of the swords and the connection between the two different spellings. 9 of these 44 were found to have the very high carbon steel and were spelled in the "+VLFBERH+T" manner. +VLFBERH+T Swords spelled in this manner have a higher carbon content (crucible steel) making them stronger and more flexible than the iron swords of the day. +VLFBERHT+ Swords spelled in this manner, and other variants, have a lower carbon content making them considerably weaker and brittle. Dr. Williams hypothesizes that these swords may have been copies or cheap knockoffs of the real "+VLFBERH+T" swords.