For any Viking enthusiast visiting a Viking fortress, when in the vicinity of one, is an absolute must. The fortress was a part of the Viking military power, and there are three other similar Viking fortresses in the area, but Trelleborg is the best preserved one. The interesting thing about these fortresses is that they are all round in shape. They were constructed around 980 A.D by King Harald Bluetooth (probably not the same guy who invented Bluetooth on your mobile phone), but evidently, weren’t used for a long period of time, only around 10 to 15 years.