Nowadays, 10th-century Danish and Norwegian King, and Viking warrior, Harald "Bluetooth" Gormsson is best remembered for lending his name to that very much 21st-century piece of cellular technology. However, this is not how the popular masses should really remember him.

Aside from seizing the crowns of the Kingdoms of Denmark and then Norway at the peak of the so-called "Viking Age" (c.793 - 1066 CE), he is also said to be the driving force behind Christianity's introduction to and adoption by a largely pagan Danish population.

By the time of his death in 986 CE, Bluetooth had consolidated his rule over what was rapidly progressing into the medieval Kingdom of Denmark. 

He was, quite literally, a nation builder and constructed a huge number of fortresses over his kingdom as well as erecting the larger of the two Jelling runic stones, a mix of Viking era political billboards, Mother's and Father's Day cards, and blatant propaganda etched into stone.

By the time of his death in about 986 CE, Bluetooth had, seemingly, crushed all his enemies and opposition to his rule. Or had he?

An anxious king

For huge parts of his reign, Bluetooth was not as secure as the history books would have us believe. 

In the south of his kingdom, a huge system of fortifications, the Danevirke, had been constructed hundreds of years before, in about the mid-7th century CE. 

These fortifications, cutting across the neck of Jutland, had been built to keep other tribes, most especially the Saxons, out of the realm of the Danes. 

Bluetooth, whilst consolidating his rule in Demark early in his career, had these series of fortifications to sure up his southern flank so he could focus further north, in Norway.

By about the mid-970s CE, however, Bluetooth had lost control of this huge area to a series of successive Saxon raids. This no doubt inflicted strategic panic and the need to reassert his authority. 

The answer was the construction of fortifications, the famous "Viking ring fortresses." Although a total of seven fortifications have been uncovered across what is now Denmark and Skåne (Sweden's southernmost province), only one (at Borgeby) is believed to have not been constructed during the reign of Bluetooth in the 980s CE.

The approximate layout of a building and Viking ring fortress in Trelleborg, Denmark. Photo: LGieger / Shutterstock

The Trelleborg fortress

Perhaps the most impressive of these fortifications constructed by Bluetooth is the Trælleborg

This fortification, excavated between 1932 and 1942 CE, is the best-known and best-preserved Viking-era fortress thought to have once controlled the sea lanes between the Danish islands of Zealand and Funen.

The fortress was designed as an exact circle, with two roads crossing at right angles. Four gates were built, with two always opposite one another. 

It is believed that the whole fortification may indeed have had a capacity for as much as 1,300 people, a seriously huge fortification in the early medieval period just before the dawn of larger Norman castles. 

A 5-meter / 16-foot-high rampart surrounded the entirety of the fortification with a diameter of 137 meters / 449 feet. Surrounding the entire fortification, unlike later castles, was not a moat but a palisade, a defensive wall made from wood.

Since its first "discovery" over 80 years ago, it has been constantly excavated. More than three mass graves and a multitude of weapons have also been found. 

Skeletal analysis suggests that most of the dead buried here are from Poland and Norway, suggesting hired mercenaries stationed at this important strategic fort. Radiocarbon dating suggests a construction date of about 980 CE with no more than a decade and a half of use.

What about a fortress at Jelling?

The town of Jelling, in Demark, is, of course, most famous for the runestones that Bluetooth, and his father, King Gorm the Old, erected in the latter stages of the 10th century CE. 

However, since 2007 CE, the Vejle Museum has been excavating the entire site. What they found was a huge palisade area, believed to cover over 120,000 m2 / 1,291,669 ft2. 

Several houses have been excavated since that time, suggesting that there may have been a royal palace situated at Jelling when Bluetooth erected the second of these runestones.

Recent radiocarbon analysis of charcoal uncovered underneath the palisade supports this approximate timeframe. Further analysis of the charcoal suggests that the palisades were made of oak which may have been cut down from the surrounding areas. 

It was believed that at the time of construction, the Royal Palace was built in an occasionally dry wetland area full of trees. The palisade would have had a height of about 4 meters / 13 feet providing yet another layer of security to the already huge fortifications. 

Given that Bluetooth had constructed as many as six fortifications across his kingdom, it seems that he left the best to last and made this Royal Palace at Jelling perhaps the most secure fortification.

Like so much of Viking history, the truth lies buried beneath our feet, and this is one excavation to keep a close eye on.

For a research paper on the architecture of the Royal Palace at Jelling, visit ResearchGate here, whilst the National Museum of Denmark has a broader article on the Jelling monuments here.

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