"When I stand here at Nonnebakken, I find myself thinking about how this great fortress must have dominated the landscape across Funen. I also think about all the archaeological finds that are still hidden and well preserved underground – a source that could give us even more knowledge about the Viking Age if we one day investigate it further."
Mads Runge, Head of Development at Museum Odense

Harald Bluetooth’s ring fortress

Nonnebakken was built around the year 980 during the reign of Harald Bluetooth and was one of the large ring fortresses constructed in several locations across Denmark towards the end of the Viking Age. The fortress measured around 180 metres in diameter and was built according to the same precise, circular principles as Denmark’s other ring fortresses.

The ring fortresses tell the story of a time when royal power was growing stronger and a king sought to unite and control his realm. Nonnebakken also stands out because of its location close to the early settlement by the Odense River – in an area shaped by people, trade and connections with the wider world.

A fortress the city grew around

For more than a thousand years, Odense has expanded across and around the old ring fortress. Today, Nonnebakken is therefore a place where history quite literally lies in layers.

You do not come here to see a reconstructed Viking fortress, but to stand on the very site where it once stood and discover the connection between the Viking Age settlement of Odins Vi and the Odense that later grew around it. The remains of the fortress are still preserved underground – in some places, just beneath your feet.

Part of the UNESCO World Heritage List

In 2023, Nonnebakken was inscribed on the UNESCO World Heritage List together with four other Danish ring fortresses: Aggersborg near Løgstør, Fyrkat near Hobro, Trelleborg near Slagelse and Borgring near Køge.

Together, they tell the story of Harald Bluetooth’s ring fortresses and the royal power that left a lasting mark on Denmark towards the end of the Viking Age. Nonnebakken is also Funen’s first UNESCO World Heritage Site.

Nonnebakken is just one of the traces left behind by Viking Age Odense. Across the city, you can discover stories of kings, churches, burial sites and ancient monuments that still connect present-day Odense with the city of more than 1,000 years ago. Download the Viking route PDF and discover more places where you can continue following the trail.