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Viking Age Ring Fortresses

Date of Submission: 30/01/2018
Criteria: (iv)
Category: Cultural
Submitted by:
Danish Agency for Culture and Palaces
State, Province or Region:
Vesthimmerland, Mariagerfjord, Odense, Slagelse and Køge Municipalities
Ref.: 6284
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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.

Justification of Outstanding Universal Value

The Viking Age Ring Fortresses are unique to Viking-Age world, and they represent the most prominent archaeological evidence of the monumental geometrical-symmetrical fortresses of the Viking Scandinavia. Five fortresses of this group are known. They have largely identical plans based on geometrical and symmetrical forms. The architecture is Scandinavian although the plan itself is inspired from Western Europe. The fortresses were distributed strategically across the Danish kingdom of that time and were built c. AD 975-80 by King Harald Bluetooth in a period of great political and religious challenges and achievements, and of technical innovation. No counterparts exist in either the Nordic Countries or Europe. The main reasons for this monumental series of fortresses is interpreted as having been defensive measures against current threats from the German empire, and the relationship to newly conquered Norway as well as means of controlling the areas under the reign of the king. However, the political situation changed, and the fortresses functioned for very few years and were left to oblivion.

Criterion (iv): The Viking Age Ring Fortresses form an outstanding and innovative example of Viking architecture, engineering, technology and a demonstration of force. They are manifestations of new centralised powers of a Viking king, and they belong to and illustrate a significant stage in North European human history. The form, layout, material and function bear witness to a time of transition in Northern Europe.

Statements of authenticity and/or integrity

The Viking Age Ring Fortresses are today prominent features set in landscapes unhampered by modern settlement. Even at Nonnebakken (situated in the southern part of the city centre of Odense) you can get a good impression to the northern part of the fortress' embankment.

All fortresses are located in landscapes typical of their respective regions with streams connecting them to the fairly close coast. At Trelleborg and Fyrkat extensive nature restoration projects have been conducted over the last decades in order to recreate the natural conditions at the time of the fortresses, while at Aggersborg and Borgring the landscape remains largely unchanged since Viking Age. The landscapes demonstrate the strategic location of the fortresses at Viking era junctions, making it possible for visitors to experience the monuments in their almost original settings.

The Viking Age Ring Fortresses were built within a short time span, used for few years for their intended main purpose and left shortly after without alterations to their layout or functions. The archaeological state of preservation and the authenticity of the five fortresses is exceptionally good and clearly demonstrate the construction and layout of the original fortresses.

The credibility and truthfulness of the evidence for the interpretation of the archaeological sites in this series is conveyed by the genuine archaeological material, as well as the construction and layout and the situation and setting of the component parts. All archaeological remains of the nominated property have retained their authentic construction and layout since the Viking Age. The archaeological material and substance of the nominated property is also entirely authentic. All building phases, features and their remains relevant to this nomination date from the Viking Age or are likely to do so. Important topographical conditions and features, which were historically availed of in the choice of site and the layout of the structures, are still recognisable even today.

Comparison with other similar properties

No similar fortresses of strict geometrical-symmetrical lay out from the Viking era exist. Therefore, it is difficult to tell what inspired the construction of the Fortresses, except from parallels to a few other at least hundred years older Dutch fortresses.

The fortresses’ unique lay-out is may be inspired from the Netherlands, where circular fortresses were constructed as protective measures in the late 9th century, such as Oost-Souburg on the island of Walcheren, while the other features of the plan are based on Scandinavian architecture which is set together in entirely new ways. Thus, the prototypes for the buildings may derive from buildings at the Jelling complex and from main buildings of contemporary rural settlements. The idea behind the fortresses and their function may be inspired from England and Germany where fortifications were an important feature of the time (cf. the English Burghal hidage, presumably from the time of Edward the Elder, and the German ‘Burgenordnung’ of Henry I). Yet the Danish fortresses constitute a unique solution confined to a specific political entity.