Harald Bluetooth and the Ring-Castle at Trelleborg

By Bethany Rogers

Castles are synonymous with the medieval period, but not all of these structures bring to mind Sleeping Beauty and knights in armor. In fact, the real-life European castle which inspires most popular imaginings of these aristocratic fortresses is Neuschwanstein, in Bavaria, commissioned by King Ludwig II and intended as a royal retreat before his death. Its graceful turrets and even crenellations in the Romanesque Revival style served as the inspiration for Cinderella’s castle at Disneyland in Orlando, Florida. The castle’s construction began in 1869 and was completed in 1886. Much of what sparks our imagination about the medieval period comes from much later sources.

By looking instead at one of the earliest castle formations in Scandinavia, we can see the development of European military culture from its inception. Trelleborg, near Slagelse, Denmark, was constructed around 980 at the height of the Viking Age. The structure shows its pedigree in its design, construction, and the grave goods and bone evidence of those who are buried within its five-meter-high ramparts. Trelleborg and the other ring-castles constructed by Harald Bluetooth (r. 958-986) stand out in history as products of a developing age of state formation, and the rising importance of military power.


The Mighty Ring-Castle

The ring-castle (or ring-fort, also called trelleborgs) at Trelleborg is an impressive structure for its size, and for the number of buildings. Its dimensions show that Harald could command vast resources in order to construct Trelleborg, and other ring-castles, including the manpower and timber to build such structures. Most ring-castles are formed by a single circle of earth, like those at Aggersborg and Fyrkat in Denmark, which is divided into four quarters. Gates were positioned at each of the compass points on this circle, and inside each quadrant of the circle were at least four longhouses constructed of wooden timbers and turf. Trelleborg had an additional, larger circular rampart made of oak, fifteen more buildings, and a cemetery; the inner circle alone measures 120 metres in diameter. Archeologist Andres Siegfried Dobat notes similarities between the Danish Trelleborg fortresses and circular fortifications in modern-day northwest France and Belgium, suggesting that the ring-castles are evidence of the importation of foreign expertise and specialized knowledge in their design and building. To date, seven ring-castles have been discovered, primarily in Denmark, but also in Sweden and Norway.

Harald Bluetooth: Castle Builder and Conqueror

Not all of them were built by Harald Bluetooth (Trelleborg near Slagelse, the aforementioned Aggersborg, and Fyrkat, and Borgeby, in Sweden are thought to be his work; other ring-castles are not conclusively dated, or are attributed to other rulers). Early research suggests those that were built by him, were training camps for warriors who were supposed to re-conquer lost Danish territories in eleventh-century England. However, T. Douglas Price, Professor of European Archaeology Emeritus at the University of Wisconsin-Madison, notes that they, “are better understood today as centres of royal power, established as a means to control and administer the provinces of the emerging Danish kingdom under King Harold [sic] Bluetooth in the tenth century AD.”


Harald claimed, in the inscription of one of the famous Jelling runestones, to have conquered all of Denmark and Norway, and to have brought Christianity to the Danes. The ring-forts in the north and east of the country were most likely one way he maintained his rule, and signaled his kingship to outlying territories with the awe-inspiring formations rising out of the landscape, bursting with trained men and goods brought from the reaches of his domain.

From the Norwegian territories he held, he amassed men and tribute, which Else Roesdahl comments came, “In the form of typical Norwegian products such as furs, falcons, iron, soapstone vessels and whetstones, all of which were sought after and could be redistributed. Through successful politics he secured the country against the German Empire, with the help of an expanded Danevirke and alliances with Slavic princes.” The multi-ethnic influence over the Trelleborg ring-castle would also be seen in the grave goods of those buried there.

Archaeological discoveries at Trelleborg

Isotope analysis of grave remains from the cemetery at Trelleborg indicates not only local Danes, but individuals from Norway and Sweden, and all across the Slavic region. In fact, more than half (67%) were not from the surrounding Danish area. Saxo, the thirteenth century Danish historian, commented in Book X of Gesta Danorum, that Harald fought off his usurper son, and his son’s supporters with an army of Danes and Slavs. This idea is supported by the ages of the garrisoned soldiers at Trelleborg, and the fact that their families and attendants were on site. T. Douglas Price et al. explains:

The Trelleborg cemetery composition more closely resembles Roman military camps and forts found in Britain and elsewhere. Cemeteries connected with these camps also show interment of sub-adults and females, but with a clear preponderance of males … This suggests that the Trelleborg fortress population was an army (mostly young adult males), but with a train including family members (resulting in some sub-adults and females in the cemetery).


Additionally, grave goods buried with the soldiers and their family members, servants, and slaves, “contain a significant number of artefacts of foreign provenance, indicating far-reaching contacts, and presumably the presence of people from more distant regions,” including a silver chest, a bronze bowl, and an axe with a silver-and-copper inlaid blade and glass beads, though most were buried with poor-quality weapons or nothing at all.

Finally, animal bone evidence excavated at Trelleborg specifically examined evidence for pre-Christian religious rituals in three wells at the site, adding to what we know went on there. Two children, both approximately four years old, and several animals, appear to have been deposited in the wells on the site in an apparent pagan sacrifice to the gods.

One recent articles on wells in Trelleborg notes:

A sacrificed young he-goat in well 47 killed during spring may be seen as a propitiatory sacrifice to honour or appease Thor and to ensure fertility. The deposition of a hindlimb of a young large-sized presumed stallion and large parts of a cow placed together with the children may also be interpreted as propitiatory sacrifices, whilst the large-sized high prestige male dog may have served a dual function as a sacrifice to the gods and a conductor for the children. The sacrificed animals showed evidence of having been deposited while still enfleshed and hence, as regards the animals normally used for consumption, constituted a resource loss to the society.


Aside from ritual sacrifice of animals, bone evidence from Trelleborg also hints at what the people who lived in the ring-castle ate, though there are relatively few samples available at the site. Of 257 mammal and bird bone fragments found at the site, only 90 could be definitively identified as cattle, sheep and goat, spanning the ninth and tenth centuries. Notably, Gotfredsen commented that, “pig and cattle bones overall exhibited the highest frequencies of butchery marks,” indicating that Trelleborg may have placed more importance on meat than dairy production; as a ring-castle, this may have been an indicator of the high social status of its inhabitants in the Viking Age, as research shows that throughout the North Atlantic, cattle and sheep were the main focus of breeding and household economy, and had more significance than other kinds of livestock.

The Decline of the Ring-Castle

Taken together, this evidence shows that, although Trelleborg was a lively place, it wasn’t used for long. Unlike the castles of Continental Europe, some of which are still used today, Trelleborg and other ring-castles built under the reign of Harald Bluetooth in the tenth century were created for a specific purpose: to demonstrate that he was king of all Denmark and commander of her army, even if some of those soldiers came from very far afield. Some of the men at Trelleborg were able to live with their families and servants, and grave goods reveal that high-status warriors also resided there. Religiously, they worshipped, depositing meat, and in two examples – small children, down the wells of the ring-castle, as possible offerings to Thor, or other Norse gods. Economically, they traded a variety of goods with allied territories, and they ate a hearty diet of meat, as suited the men of a king who was determined to show his power and largesse through these huge fortresses on the coast of Denmark and Sweden.

Beth Rogers is a PhD student at the University of Iceland, where she works on the cultural significance of dairy products in the Middle Ages. You can follow her on Twitter @BLRFoodHistory

Click here to read more from Beth Rogers

Further Reading:

Anne Birgitte Gotfredsen, Charlotte Primeau, Karin Margarita Frei and Lars Jørgensen, “A ritual site with sacrificial wells from the Viking Age at Trelleborg, Denmark,” Danish Journal of Archaeology 3:2 (2014)


T. Douglas Price, Karin Margarita Frei, Andres Siegfried Dobat, Niels Lynnerup and Pia Bennike, “Who was in Harold Bluetooth’s army? Strontium isotope investigation of the cemetery at the Viking Age fortress at Trelleborg, Denmark,” Antiquity 85 (2011)

This article was first published in The Medieval Magazine – a monthly digital magazine that tells the story of the Middle Ages. Learn how to subscribe by visiting their website.

Top Image: Trelleborg – Photo by Thue C. Leibrandt / Wikimedia Commons