Fyrkat Viking Fortress is located in a valley near the town of Hobro in Denmark. Fyrkat was a major concentration of manpower in Viking times.
Inside Fyrkat were four groups with four houses in each. There were no fireplaces in any of the houses implying that people lived outside using the fortress only for defense.
Like others found, Fyrkat is located next to a waterway, but so far up the fjord that you had to know it was there and then had to look it to find it.
The concrete marks post holes.