I agree that Skien certainly 'became' a commercial center.? However, as your article reference notes, until 1979 it was believed that it was not founded until the 1300s when it became a market town.? Since then archeology found that it's history did go back to the Viking age (800s) when it was a meeting place for farmers inland.
I don't see anything to suggest that Skien was of any significant size in terms of population in the 800s.? Some estimates have the total population of Norway as between 100,000 and 150,000 at the start of the Viking age.? A meeting place for farmers in rural Norway does not suggest it seeing a lot of travellers from other countries.? Norway was pretty isolated until they revolutionized their boats and Vikings became a dominant force.? The fact we know so little of Norway before the Viking age attests to that.? This would give 700 years of isolation (from 86 CE for R-S5245 clades) till a few years before 793 CE when Lindisfarne was attacked.? No doubt that the area rapidly expanded after that as Halfdan the Black and the kings of Dublin are said to have come Vestfold.? Wealth would have been now pouring into the area.
