Ulfberht is a modern transcription of the inscription +VLFBERH+T, which is typically found on early medieval Norse and Germanic swords of the 8th to 11th centuries. Many variations of the inscription exist, such as +VLFBERHT+ or even VLFBERH+T.
It is generally assumed that it originally referred to a Frankish blacksmith, whose name and workshop later established a kind of trademark.
Most swords are classified as Type X according to the Oakeshott classification, although the transition to high medieval sword forms is rather fluid. Also, almost all period-typical handle designs according to the Petersen vessel typology are found.
According to the classification of swords by Alfred Geibig there is also no uniformity. It can be assumed that this inscription was used over several centuries, and not only by a single workshop or person.
The nature of the inscription (the presence of cross symbols before and after the actual letters) also allows conclusions to be drawn about the origin and meaning of such markings.
The fact that most of the swords with the inscription "Ulfberht" were found in Scandinavia testifies to pronounced trade relations between the Frankish Empire and Northern Europe. There is evidence of finds from Eastern Europe and even from the Near East, often with vessels (guard, hilt and pommel) that corresponded to local customs.
However, the vast majority of blades come from the area of the Rhine Franks, which already had a distinctive metallurgy in the Latène period.
The exact origin is unclear. Some researchers assume that the steel originated in Afghanistan, Persia or India. It is said to have reached Europe via traders from the Orient via the Volga and the Caspian Sea.
Material analyses, on the other hand, indicate that the lead originated in the Rhenish Slate Mountains. Therefore, some researchers suspect the monasteries of Fulda and Lorsch as places of production.
There is circumstantial evidence for this after a find in 2012. During dredging work, a very well-preserved Ulfbehrt sword was found in the Weser River near Hessisch Oldendorf.
After a detailed analysis, the State Office for the Preservation of Historical Monuments in Lower Saxony and the University of Hanover came to the conclusion that the sword was forged in the 10th century and that the lead used in the handle came from the Hintertaunus region.
This was therefore taken as an indication of a workshop in Fulda or Lorsch, because weapons production there is vouched for in each case and other monasteries would presumably have fetched the lead from closer deposits.
Since only one of the other 170 or so swords found bears a resemblance to the one from Hessisch Oldendorf, however, researchers suspect that it is a late example that merely used the "brand name".
The results of modern metallographic research prove that the early medieval Frankish-Alemannic swords were top-quality products in their time, produced at the highest level of craftsmanship.
Stefan Mäder's work proves that the damascened swords of the early Middle Ages often had a highly complex structure and were selectively hardened.
In addition, the research results of Alan Williams have shown that the "Ulfberht" specimens are made of steel that is of good quality even measured by today's standards.
These results are consistent with the metallographic data of the sword from the Essen Cathedral Treasury, which is made of pattern-welded steel that has very low levels of sulfur and phosphorus and a peak carbon content of 1.1%.
The construction of early medieval blades was highly variable: there were simple carburized iron swords and complex composite blades. On damascened swords, the cutting edges were often welded separately to the body, which was formed from torsion damascus.
Late Carolingian swords with the +VLFBERH+T inscription, however, generally had no visible damascus structures; by this time, the increasing abandonment of complex damascus decoration due to improvements in racing furnace technology was already beginning.
It can therefore be assumed that the value of the "Ulfberht trade mark" resulted from the advanced racing furnace and forging technology of the time.
The actual inscription was then welded into the body of the blade using red-hot iron wire or other materials.
The above-mentioned characteristics and the metallurgical knowledge of the early medieval smiths made the swords "high-tech weapons" of the time, which led to the appreciation and preference of certain products. Besides +VLFBERH+T, other inscriptions are also known, such as LEUTFRIT, BANTO, UGTHRED or INGELRII (also INGELRED).
Williams interpreted the measured carbon content of about 1.0% as an indication of the use of crucible steel. In contrast, this carbon content could also be detected in the ceremonial sword of the Essen cathedral treasure, which is made of native ferrous steel.
The uniform distribution of carbon in European steel (unlike carburizing iron, where only the surface of the material becomes rich in carbon) has been demonstrated by sword researcher Stefan Mäder, among others.
According to J. D. Verhoeven, carbide formers such as vanadium and molybdenum in significantly increased amounts up to 0.3% are typical for special Indian iron ores, which were also detected in original Wootz blades. This evidence remains absent in European blades to this day.
It is also claimed that the cutting edges and the core of the "Ulfberht" swords were uniformly made of steel, while conventional swords had an iron core and steel cutting edges.
The latter is not true, since in Europe already in the course of the 10th century damascening was increasingly abandoned and blades were made only of refined steel, with evidence of both all-steel swords and composite blades.
Also, from the 11th century onward, high quality steel was available in greater quantities, due to improvements in racing furnace technology.
To date, there is no reliable evidence for the use of crucible steel in European weapons. As confirmed by recent research results, the low amounts of slag and so-called "steel pests" (e.g. sulfur and phosphorus) as well as the high content of carbon and its uniform distribution could also be achieved with lightening furnace technology available in the period in question.