Researchers have discovered that a major medieval monument has been hidden in plain-sight for centuries in the heart of Derry City, making it the only medieval structure still standing in the city.

The monument, which stands in the grounds of Lumen Christi College, was previously thought to be the remains of a 17th century windmill tower. However, researchers from the School of Natural and Built Environment at Queen's have discovered that the monument is actually over 300 years older, dating from the 13th or 14th centuries AD, and is most likely the remains of a "lost" monastic round tower.

Speaking about the significance of this find, Dr Colm Donnelly, Director of the Centre for Archaeological Fieldwork at Queen's commented: "This monument is the only medieval structure still standing in Derry. All other medieval buildings that were once here are now gone, buried under the centuries of building activity that have happened in the city over the past 400 years."

Dr Gerard Barrett, Research Fellow from the School of Natural and Built Environment at Queen's, made the discovery through radiocarbon dating of mortar retrieved from the building, as part of innovative research underway at the 14CHRONO Centre for Climate, The Environment and Chronology at Queen's. Radiocarbon dating of mortar is a new method for determining the age of a building. It works by measuring how much of the radiocarbon (an isotope of carbon) that was trapped when the lime mortar originally set still remains, centuries, or even millennia later.

Dr Barrett explains how he discovered that the monument was actually a medieval building: "The radiocarbon dates we obtained suggested that the fabric of the tower was from the medieval period. The work that local historians in the Derry Tower Heritage Group had previously carried out suggests that a medieval round tower once existed in this general location in 1600. 

"By 1685, however, the round tower is no longer shown on any historic maps, but a windmill is shown on the outskirts of the city. The radiocarbon dates are not saying that the tower wasn't reused as a windmill in the 17th century, but it would seem that the 17th century builders were making-do and mending, using the stump of the old round tower for a new purpose."

The new scientific dates have been welcomed by the Derry Tower Heritage Group, whose members have been studying the history of the tower for the last five years and who had the foresight to have the mortar sample collected from the building during conservation work in 2013.  

Stephen Doherty, member of The Derry Tower Heritage Group and teacher at Lumen Christi College said: "The new discovery is set to change our understanding of the early history of Derry. The textbooks will certainly need to be revised. Up to now we had no upstanding medieval fabric surviving in our city - now we have a round tower."

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Media inquiries to Jemma Greenlees at Queen’s University Communications Office T; +44 (0)28 9097 5821 E: j.greenlees@qub.ac.uk.