Archaeologists have discovered the almost complete remains of a long-lost medieval church choir beneath the heart of Oslo — without lifting a shovel.
Ground-penetrating radar (GPR) surveys at Oslo Hospital have revealed the choir of a former Franciscan monastery church, together with what may be the foundations of an altar, traces of a brick-floored room and possible graves belonging to a forgotten cemetery.
The discovery by the Norwegian Institute for Cultural Heritage Research (NIKU) demonstrates how modern geophysical technology is allowing archaeologists to investigate buried sites without immediately resorting to excavation.
The Oslo findings are among a series of discoveries featured in the newly published book Archaeological Geophysics in Norway, which traces the development of archaeological geophysics in the country from early experiments in the 1960s to today’s sophisticated motorised radar systems.
A lost monastery beneath modern Oslo
The site at Oslo Hospital has more than 700 years of history.
Franciscan friars established a monastery there around 1290. Following the Reformation, the monastery was converted into a hospital in 1538 on the orders of King Christian III.
Although archaeologists have investigated the site for decades, important parts of the monastery complex remained elusive. In particular, researchers had been unable to establish a complete picture of the church choir.
That changed when NIKU conducted GPR surveys across gardens and streets surrounding Oslo Hospital in 2018 and 2023.
Radar signals revealed buried structures immediately beneath the modern surface. Among them was an unexpectedly clear outline of almost the entire monastery church choir.
Researchers also identified features that could represent the remains of an altar foundation and a room containing a brick floor.
Perhaps most intriguing were several structures resembling graves. Their presence supports the theory that the area immediately north of the monastery church once served as a cemetery.
Modern infrastructure makes interpreting the site particularly difficult. Trenches, pipes and cables cut through the archaeological landscape and can obscure older structures.
Nevertheless, the research demonstrates that combining geophysical evidence with historical records can allow archaeologists to reconstruct surprisingly detailed pictures of sites hidden beneath modern cities.
Seeing archaeology without digging
Ground-penetrating radar works by transmitting electromagnetic pulses into the ground and recording reflections produced when those signals encounter changes beneath the surface.
Walls, foundations, graves, ditches and other archaeological features can generate recognisable anomalies within the resulting data.
Rather than exposing those structures physically, researchers can use the measurements to build an image of what lies underground.
The Oslo monastery is far from the only major Norwegian archaeological discovery made using the technique.
GPR has played an important role in identifying buried Viking ships, including the Gjellestad ship in Østfold and the Edøy ship in Møre og Romsdal. Researchers have found that individual vessels can produce distinctive shapes or “signatures” within radar data.
But the technology is also revealing less spectacular — and archaeologically important — evidence of everyday prehistoric life.
An Iron Age house hiding in a ‘blind zone’
One of the clearest examples comes from Sola in Rogaland, where researchers from the Archaeological Museum at the University of Stavanger used GPR before excavation.
Traditional archaeological evaluations frequently employ trial trenches. By stripping away soil along selected sections of a site, archaeologists can determine whether significant remains survive underground.
The limitation is straightforward: only part of the landscape is physically examined.
At Sola, the radar survey covered a substantially larger area than previous trenches. The results revealed something the earlier investigation had completely missed — a prehistoric three-aisled longhouse dating from the Iron Age.
Remarkably, the entire building lay between two previously excavated trial trenches.
It had effectively survived within a blind spot created by the sampling strategy.
The case demonstrates one of the principal advantages of archaeological geophysics. Instead of examining isolated sections of a landscape, researchers can survey large areas and identify relationships between structures that might otherwise remain invisible.
GPR does not mean the end of excavation
Despite its potential, researchers emphasise that ground-penetrating radar is not a replacement for archaeological excavation.
Radar can indicate where buried structures are located and reveal their approximate form, but excavation remains necessary to examine archaeological layers directly, recover artefacts and collect material for scientific analysis and dating.
Instead, the two approaches can complement one another.
Geophysical surveys can provide archaeologists with a detailed map before excavation begins, allowing them to position trenches more strategically and concentrate resources on areas most likely to answer important research questions.
That can mean fewer unnecessary trenches, better sampling and a clearer understanding of how individual finds relate to buildings and other archaeological features.
The result is a shift from searching largely through selective excavation towards increasingly targeted investigation informed by a broader view of what survives underground.
Decades of Norwegian geophysical archaeology
The Oslo monastery discovery is featured in Archaeological Geophysics in Norway, released on 25 August 2026 by Cappelen Damm Research.
Edited by Knut Paasche, Petra Schneidhofer and Arne Abel Stamnes, the book brings together contributions from 16 specialists and provides a comprehensive account of archaeological geophysics in Norway.
The project is a collaboration involving NIKU, the Archaeological Museum at the University of Stavanger, Vestfold County Municipality, Møre og Romsdal County Municipality and the NTNU University Museum.
It charts a technological transformation that has taken archaeological geophysics from relatively limited experiments in the 1960s to large-scale surveys conducted with modern motorised ground-penetrating radar equipment.
The discoveries presented in the volume point to the same broader conclusion: archaeological sites do not always need to be excavated before their outlines can be understood.
At Oslo Hospital, centuries of construction, roads and modern infrastructure had concealed a substantial part of a medieval religious complex. Yet beneath those layers, the footprint of the Franciscan monastery survived.
More than 700 years after the friars established themselves there, modern radar has made the forgotten church visible again — while leaving the archaeology safely underground.
Header Image Credit : Jani Causevic, NIKU
Sources : Niku
