About 500 BC iron technology was introduced in Denmark and during the following 1500 years iron was produced in all regions of the local bog ore. The bloom was the first product of the farmers’ furnace, a mixture of iron and slag, which it was necessary to gather and weld to a denser billet. Low-carbon zones could alternate with medium- and even high-carbon zones in one and the same piece of iron. And phosphorus-rich zones is very often interspersed in billets and artefacts found in Denmark. Most certainly the blacksmiths were able to identify and separate carbon-rich and phosphorus-rich parts of the bloom and to secure these for specific purposes. And although most tools and weapons were forged using the low-carbon iron the smelter knew how to produce high-carbon iron containing about 0.6–0.8 % C from the bog ore. Typological and metallurgical analyses of iron knives are an excellent way to study the production, distribution and consumption of iron. From the earliest rather large pre-Roman knives with straight back and a wide, hanging edge, it is possible to trace change and development through thousand of knives to the small knives with a tang offset from the middle of the blade found in the Viking Age graves. Some knives are only found in association with female burials. Other knives are only found in association with weapons, others again only in some parts of Denmark. The evidence from the first 500 years of iron forging in Denmark leaves us with the impression of capable and skilled craftsmen with plenty of low-carbon (less than 0.35% C) iron at their disposal. Very large knives were rarely forged in the Danish smithies of the 4th and 5th centuries. At this time, smaller curved and straight knives were preferred. A 25 g billet would, on average, have been enough for each knife. But somewhere in the 6th or 7th century there seems to be a marked change in the forging-techniques in Denmark and the use of the different bloomery irons becomes more complex. The billets of local iron often combine in the same knife with iron exchanged from a distance. The shift in technology is seen as high-carbon iron now plays a more important role. Although there are some early examples of knives forged exclusively of iron from the Scandinavian peninsular found in the 3rd century war booty sacrifice at Illerup Ådal. Many of the really large, single-edged knives in the 7th century have a blade length about 20 cm. They were often forged with a tang offset from the middle of the blade and a distinct shoulder between blade and tang. The large knives are found exclusively in male graves and are often placed by the hip of the dead together with a much smaller knife. Although no organic material is preserved, it is likely that the two knives originally were carried together in lined scabbards with additional sheaths. In the same graves, by the other hip, or close to shield and lance, lies a single-edged sword. Close studies of the knives and the sword show no marked difference between the large and the small knives. They are both forged of low-carbon iron while the swords are all forged using low- and high-carbon iron. A special interest is often paid to the three-layer knife (the knife forged in the so-called sandwich-technique). These knives (Fig. 1) are the most common knives to be found in the Danish Viking Age. And from the end of the 9th century, throughout the 10th century and the beginning of the 11th century knives were mainly forged using this technique in Estonia, Latvia, Lithuania, and Sweden – and in the Western regions of Russia. The same forging technology has been registered in knives found in England, but there they apparently never occur quite as often as in Scandinavia. In central Europe knives were rarely forged in this way, although the technique was used for other edged implements. The by now oldest known knife in Denmark forged in this technique is found at Lousgaard a cemetery at the Baltic island Bornholm. This grave is dated to the early 7th century and the slag inclusions in all billets show rather similar values, among others low values of phosphorous oxide and high values of aluminium oxide. That indicates that the knife might have been forged from a Swedish or Norwegian ore. On the contrary, the iron in the Langsax – found in the same grave – contained 0.5% phosphorus and the slag inclusions show very similar values – among others high values of phosphorous oxide and minimal values of aluminium oxide. These values indicate that the sword was forged of iron made of bog ore, most likely dug up in the northern most parts of Germany or in Western Jutland. Even though the social organisation around the production and the consuming of iron in Denmark never seems to reach the same level of specialisation as have been seen around sites in other parts of Northern Europe, the local bog ore was smelted and forged according to the way it was done in the neighbouring countries. And the knife from Lousgaard is a good example on the marked change in the forging-techniques and in the use of the different quality of bloomery irons that took place in the Late Iron Age.