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.
The Viking Age Ring Fortresses are distributed over the then kingdom of Denmark. They include Fyrkat near Hobro in northern Jutland, Aggersborg near Løgstør in mid Jutland, Nonnebakken in Odense on the island of Funen, Trelleborg near Slagelse and Borgring near Køge on the island of Sealand.
Fyrkat 56°37’23″N 9°46’13″E
Aggersborg 56°59’43″N 9°15’17″E
Nonnebakken 55°23’32″N 10°23’18″E
Trelleborg 55°23’38″N 11°15’54″E
Borgring 55°28’10″N 12°7’20″E
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.
The fortresses were, however not entirely identical. For example: some differed in size – the largest being Aggersborg with an inner diameter of 240m, while Trelleborg’s inner diameter is c.136m, and the diameter of Fyrkat, Nonnebakken and Borgring is 120m – half of Aggersborg’s. Further, Trelleborg had an outer ward with 15 houses. Cemeteries are known next to Trelleborg and Fyrkat.
The fortresses are known exclusively from archaeology. Their construction is precisely dated by dendrochronology, radiocarbon dates and artefacts to c. AD 975-80, and they functioned for very few years. Except for Nonnebakken, which today is situated in an urban setting, the sites were, until excavation, only disturbed by agriculture. There are, therefore, unique possibilities to study the remains of buildings and other constructions, and life at the fortresses, while further information is gained from the two cemeteries. Also, at Nonnebakken much of the fortress is preserved and a recent excavation shows that this certainly is true for the northern and northwestern part. Evidence shows that women and children also lived in or at the fortresses as well as craftsmen of various professions – not just warriors. At Fyrkat a female grave belonged to a pagan sorceress, despite Denmark’s official conversion to Christianity c.15 years before the fortresses were built – demonstrating the King’s policy of religious tolerance. At Aggersborg, Fyrkat and Trelleborg excavations has documented regularly placed groups of four identical longhouses arranged in quadrangles. The buildings (longhouses) were c.30 m long and of identical plan and shape, although their function differed; some were living houses, while others were workshops or for storage. Closely related buildings have been identified at rural settlements, but there is no trace of agriculture at the fortresses. They stand apart from the rural subsistence economy and would have relied upon the surrounding settlements for basic resources.
The fortresses are an important part of a series of great buildings works by King Harald Bluetooth (king c.958-87) manifesting the range and power of the king. The ring fortresses stringent uniformity are the persuasive gesture of a royal power both emphasizing extraordinary visions of authority and shielding the realm from external threats. The unambiguous standardization of the strongholds and their widespread distribution throughout the kingdom is unparalleled.
Other important building works by Harald Bluetooth include the dynastic Jelling monuments (World Heritage List – Jelling Mounds, Runic Stones and Church, ref. 697), the Ravning Enge bridge, extensions of town walls, and – probably – the rampart Kovirke, which is part of the border wall, the Danevirke (World Heritage Tentative List – Hedeby and Danevirke, an archaeological border landscape, ref. 5591). Except for the town walls, all were innovative, huge, based on geometric forms and had a very brief active periode of use.