King Harald Bluetooth
In Denmark, archaeologists have discovered the remains of a 1,000-year-old Viking fortress
that may have been built by King Harald Bluetooth.
http://www.archaeology.org/news/2500-140909-denmark-viking-ring-fort
Come explore more! Subscribe to Archaeology magazine: http://bit.ly/1l8PJQ8
Mentioning a magazine in a way that looks like advertising is not wise.... still, this is interesting material for us followers of saga history, so I'll repeat it:
http://www.archaeology.org/news/2500-140909-denmark-viking-ring-fort
"Late tenth century" (950-999) fits with our current estimates on Harald "Blue Tooth", king of Denmark, which is 910-986.
the viking trenches in ireland are interesting too: http://archive.archaeology.org/1101/trenches/viking.html