At https://archaeologynewsnetwork.blogspot.com/2017/09/the-enigma-of-early-… … Norwegians made top quality iron products but where did they get the knowhow? For centuries people in the middle of Norway made huge amounts of first class iron out of bog ore. Presumably this is where the bogs were located – and the same situation prevailed in Sweden. They made tools and weapons, more than the needs of the locals as Norway is a pretty low populated country. This indicates much of the production was exported – but to where? Significantly, production appears to peak in around AD200, when the Roman empire also peaked. The big question that has flummoxed investigators in the past is – where did they get the expertise? How did the technology reach barbarian Norway (or Scandinavia in general).
Archaeologists in Austria have unearthed a furnace with exactly the same measurements and design of those in Norway – hundreds of miles away, and at that time within the boundaries of the empire. The furnace dates from AD100, contemporary with those in Norway. It is an exact copy of Norwegian furnaces and although the slag pit is built of clay (in Austria) rather than stone (in Norway) the similarity stands.
It is thought the technology to extract iron and smelt it must have come from outside Norway – and the Roman empire is the obvious culprit (if that is the right word). They had the skills. Iron production is known 4000 years ago in what is modern Turkey (Anatolia). Iron plates were found in one of the pyramids in Egypt (even earlier) but most importantly, the Etruscans were the first Europeans to produce iron it is thought, and a) they hailed from Anatolia (or at least a ruling elite), and b) the Etruscans controlled Rome in its early years. The Celtic people went on to improve iron production by introducing carbon – producing steel. The technology spread rapidly throughout the empire, including Syria and Damascus (famous somewhat later for its steel swords). The barbarians of Scandinavia could have brought back the knowledge from the empire (during the course of trade relations, such as exchanging Baltic amber for iron etc), or it was disseminated by Celtic and Germanic tribes subsumed into the empire but maintaining contact with the barbarian north. Good inventions rarely remain secret for very long.
… In Norway iron was made from bog ore. It is not known if the Romans used bog ore but it is likely that Iron Age people in Britain and Ireland did make use of bog iron – and learnt about other iron ores after the arrival of the Romans. Bog ore was gathered in spring and the smelting took place in the autumn. There are hundreds of places in Norway where evidence of iron production has survived. Slag heaps are common archaeological discoveries. As Scandinavia was frozen in the Late Glacial Maximum it had a reservoir of bog iron. The same situation prevailed in Britain no doubt but it is a moot point whether Iron Age people exploited it or ore seams such as occur in Northants.