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| Image Credit : Peruvian State |
The Discovery
A medieval monastery complex believed to have been almost completely destroyed following the Reformation has been discovered beneath a football pitch in Denmark, with ground-penetrating radar revealing remarkably well-preserved buildings about a metre below the surface. Archaeologists surveying a sports field at Byparken in Roskilde have identified extensive remains of the 13th-century St Clara Monastery, including its church, cloisters, individual rooms and structural foundations.
The investigation was commissioned in connection with plans to construct an underground parking facility beneath the sports field. Historical records had established that a medieval nunnery once occupied the area, prompting Danish museum organisation ROMU, which includes Roskilde Museum, to investigate before development proceeded. Rather than immediately excavating the site, archaeologists turned to ground-penetrating radar, or GPR, a non-destructive technique capable of mapping buried structures without disturbing them.
What Archaeologists Found
"We knew that the monastery of Saint Clara had been located here, but not how much of the facility from 1256 had been preserved," ROMU archaeologist Jesper Langkilde said. "The georadar survey has provided very clear results and a good basis for planning further investigations." The survey was carried out during a snowy day in January 2025, as researchers systematically crossed the football pitch with radar equipment. The results have since revealed that substantial sections of the monastery survive approximately one metre beneath the modern ground level.
The investigation was conducted through a collaboration between ROMU, the National Museum of Denmark and the Norwegian Institute for Cultural Heritage Research, known as NIKU. NIKU archaeologist Arne Abel Stamnes carried out the GPR measurements, and the resulting images reveal the fundamental layout of the monastery with remarkable clarity. Researchers can distinguish four wings arranged around a central courtyard, together with internal room divisions and cloisters. The monastery church has been identified within the southern wing, while the eastern wing appears particularly well preserved, showing clear evidence for rooms and foundations associated with vaulted architecture. The northern wing also survives strongly in the radar data, and additional signals suggest the presence of further buildings and structures outside the main monastic enclosure.
Historical Background
St Clara was one of five monasteries that helped establish medieval Roskilde as an important centre of ecclesiastical and royal power. The nunnery was founded in 1256 and survived until the upheavals surrounding the Reformation in the 16th century, after which its buildings were dismantled and demolished. Historical accounts indicate that around half a million bricks from the complex were sold for use at Selsø Castle, a scale of demolition that led generations of researchers to assume little or nothing of the monastery remained.
Modern development across Roskilde has also left archaeologists with limited evidence for the appearance and organisation of the city's medieval monasteries more broadly. The unusual survival of an undeveloped open space directly over St Clara has now provided an opportunity to investigate a monastery on a scale rarely possible within a modern city environment.
Scientific Analysis
Ground-penetrating radar allows archaeologists to investigate buried sites without initially disturbing them. A radar scanner sends electromagnetic waves into the ground as the equipment is moved systematically across the survey area. When those waves encounter features with physical properties different from the surrounding soil, such as stone or brick walls, foundations, trenches or other evidence of human activity, part of the signal is reflected back toward the instrument. Researchers then process thousands of these measurements to produce horizontal "slices" through the ground at different depths, and in favourable conditions, the resulting images can reveal the position and shape of buried archaeological structures with considerable precision. At St Clara, the technique effectively produced a plan of the monastery without archaeologists having to expose its walls.
Stamnes described the results as unusually striking. "The results are simply impressive," he said. "GPR data does not always provide such clear images, and interpretation often requires extensive analytical work." In Roskilde, however, researchers were able to recognise archaeological structures while they were still collecting the data. "This is the first time I have documented such a well-preserved monastery complex with ground penetrating radar, and in my opinion, these are among the clearest ground penetrating radar results from a monastery complex in Scandinavia," Stamnes added.
NIKU building archaeologist and medieval monastery specialist Regin Meyer echoed this assessment, describing the depth slices of the monastery as "an exceptionally good georadar result over a monastery complex." Meyer explained: "You see four monastery wings perpendicular to each other as a frame and boundary for a monastery courtyard. It is also incredible that so much architecture can be read from the georadar material, with a number of room divisions, pillar foundations and characteristic cloisters." Possible structures outside the principal monastery quadrangle have also been detected, which could prove important not only for understanding the monastery itself but also for reconstructing the wider landscape in which the religious community once operated.
Why This Discovery Matters
The significance of the discovery is heightened by St Clara's unusual legal and archaeological status. It is the last of Roskilde's five known medieval monasteries to be investigated in this way. The other four monastery sites are protected, while the St Clara area has not received the same protection, because its archaeological remains were long believed to have been lost entirely. The new evidence demonstrates that substantial medieval architecture in fact survives beneath the site.
Meyer said the results highlight the broader value of geophysical techniques for identifying archaeological remains before excavation takes place. "The dataset clearly shows the architectural archaeological potential that lies beneath the ground surface at this site," he said, noting that the survey provides both a tool for protecting the surviving architecture and a foundation for more precisely targeted archaeological investigation going forward.
What's Next?
The monastery will not remain entirely untouched. The next stage of the project is expected to involve archaeological test trenches in the part of the site affected by the proposed underground parking facility. Researchers will compare evidence from those excavations with the GPR results to determine the condition, depth and character of the buried remains. That information will then guide decisions about whether larger archaeological excavations are necessary, and how the planned development could proceed without destroying the most important surviving sections of the monastery.
For archaeologists, the priority going forward will be to document the complex thoroughly while finding ways to preserve its best surviving elements for the future, balancing the practical needs of the parking development with the exceptional archaeological value now confirmed to lie beneath the site.
Conclusion
What had been regarded as an essentially lost medieval monument has emerged as an unusually complete archaeological site, hidden not beneath later buildings, but just a metre below an ordinary Roskilde football pitch. As archaeologists move toward targeted test excavations, the remarkably clear ground-penetrating radar results from St Clara Monastery stand as a powerful demonstration of how non-invasive survey technology can rewrite assumptions about what survives beneath even the most unremarkable modern landscapes.
Sources : Peruvian State
FAQ
Q: What was discovered beneath the football pitch in Roskilde? A: Archaeologists identified extensive, well-preserved remains of the 13th-century St Clara Monastery, including its church, cloisters and structural foundations, roughly a metre below the surface.
Q: How was the monastery found without digging? A: Researchers used ground-penetrating radar (GPR), a non-destructive technique that maps buried structures by sending electromagnetic waves into the ground and analysing the reflected signals.
Q: Why was the monastery believed to have been lost? A: St Clara was dismantled after the Reformation, with around half a million bricks sold for use at Selsø Castle, leading researchers to assume little or nothing of the complex survived.
Q: What does the radar data show? A: It reveals four monastic wings arranged around a central courtyard, along with room divisions, pillar foundations, cloisters and possible structures beyond the main monastic enclosure.
Q: What happens next at the site? A: Archaeologists plan targeted test excavations to verify the GPR findings before deciding how the proposed underground parking development can proceed without damaging the monastery's best-preserved sections.
