The monastery was lost. Archaeologists have now found it beneath a football pitch

The investigations were carried out in connection with plans to build an underground parking facility beneath the sports field at Byparken in Roskilde.

Historical sources state that a convent for nuns stood at the site during the Middle Ages.

For this reason, Roskilde Museum (ROMU) wanted to examine the area more closely using ground-penetrating radar (GPR). The method is quick and non‑destructive. It can map structures below the ground without excavation.

“We knew that St Clare’s Convent had been located here, but not how much of the complex from 1256 had been preserved. The GPR survey has produced very clear results and a solid basis for planning further investigations,” says archaeologist Jesper Langkilde at ROMU.

Thought the monastery was lost

In the Middle Ages, St Clare’s was one of five monasteries that made Roskilde an important town. Both ecclesiastical and royal power were centred here for many years.

It has long been known that the convent was dissolved and demolished after the Reformation in the 16th century. Half a million bricks were sold to Selsø Castle. Because of this, it has also been assumed that nothing remained of the complex.

Urban development has meant that today we have only limited knowledge of what the monasteries in Roskilde looked like.

The fact that the discovery was made beneath an open grassy field that has not previously been developed provides a fantastic opportunity to learn more about St Clare’s Convent and the area in which it stood, explains archaeologist Langkilde.

Exceptionally good GPR results

GPR works by sending electromagnetic waves into the ground.

When the waves encounter structures with properties different from the surrounding soil, such as masonry or other traces of human activity, the signals are reflected back to the receiver.

The results can then be processed into detailed maps showing what lies hidden beneath the surface.

The mapping in Roskilde revealed traces of the monastery buildings, including room divisions, cloisters, and a church in the southern wing.

The eastern wing in particular appears to be very well preserved, with clear traces of both vaulting pillars and room divisions.

“The results are simply impressive. GPR data does not always provide such clear images, and often the interpretation requires extensive analytical work,” says Arne Abel Stamnes, an archaeologist at NIKU. He has extensive experience with geophysical surveys of cultural heritage sites.

Stamnes says they could already see the structures while they were driving around the football pitch.

“This is the first time I've documented such a well‑preserved monastery complex with GPR. In my assessment, these are among the clearest GPR results from a monastery complex in Scandinavia,” he says.

A unique basis for further investigations

NIKU’s building archaeologist and monastic expert Regin Meyer agrees with the assessment.

He explains that they can see four monastery wings positioned at right angles to one another, forming the frame and boundary of a cloister courtyard.

“It's also remarkable that so much architecture can be interpreted from the GPR material. We can see several room divisions, pillar foundations, and characteristic cloisters,” says the archaeologist.

Meyer believes it is likely that further investigations will reveal additional buildings that still lie hidden underground.

May provide new knowledge about medieval Roskilde

St Clare’s Convent is the last of the five medieval monasteries known from Roskilde.

The other four are protected heritage sites, while the area where St Clare’s Convent is located is not protected. This is because it was long assumed that the cultural heritage remains had been lost.

The next step will be archaeological investigations in the area where the parking facility is planned.

Together with the GPR results, these investigations will provide a basis for further planning of possible archaeological excavations.

The aim is both to document the cultural heritage and to find solutions that can ensure that the best‑preserved parts of the monastery are preserved for the future.

GPR in archaeology

Ground‑penetrating radar (GPR) is used to map structures below the ground without excavation.

A GPR scanner mounted on an ATV is driven systematically over an area while it sends electromagnetic signals down into the subsurface. When the signals encounter, for example, masonry, ditches, or other structures, they are reflected back and recorded by the instrument.

The method can provide very precise results and help archaeologists identify areas that should be examined more closely through excavation.

Geophysics at NIKU

NIKU has almost two decades of experience in research, development, and use of geophysical methods in archaeology.

NIKU has previously been a partner in the large international research institute Ludwig Boltzmann Institute for Archaeological Prospection (LBI ArchPro) in Austria, which has now concluded, as well as in an ongoing collaboration with Geosphere Austria and the Vienna Institute for Archaeological Science (VIAS).

The combined experience is now being carried forward in research and heritage management in Norway and abroad, including NIKU’s projects carried out together with the National Museum of Denmark.

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