Spread across Denmark are a series of similar fortresses built by the Vikings within a very limited timeframe and with a remarkable symmetry. The fortresses are some of the most prominent archaeological remains from the Viking Age in Denmark. [youtube]6a2Yvwiu0jU[/youtube]

The Viking Age Ring Fortresses have a uniform and stringently geometrical-symmetrical architecture characterized by an exactly circular rampart, concentric ditches, and gates at the four points of the compass. The gates establish the internal division of each fortress into four quadrants. If the terrain chosen did not meet the demands of the geometric plan, great infillings were made. The building materials were grass turf, timber, earth and in some cases stones. (whc.unesco.org/en/tentativeli…)

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Fyrkat is a former Viking ring castle in Denmark, dating from c. 980 AD. It is located near the town of Hobro, some distance from the present end of the Mariager Fjord in Northern Jutland. The fortress is built on a narrow piece of land, with a stream on one side and swampy area on the other sides. It would have enabled control of the traffic on the main land route between Aalborg and Aarhus.

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The inner diameter of the ramparts was 120 meters and the width at the base 12–13 meters. They were constructed of three rows of vertical wooden poles. Each pole connected to the next ring by beams.

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