Archaeologists from the University of Chester have made an unexpected medieval discovery beneath Chester Castle in England, uncovering the remains of an 800-year-old bridge without turning a single spade of earth.
The find was made during a high-tech digital survey of the castle complex, where researchers employed laser scanners, drones and advanced 3D modelling to document the site above and below ground.
The breakthrough came when Professor Stewart Ainsworth, landscape archaeologist and Visiting Professor at the University of Chester, explored the surviving underground passages beneath Chester Crown Court, which occupies the site of the castle’s former 18th-century prison.
While investigating a narrow corridor, Professor Ainsworth noticed a section of masonry unlike the surrounding Georgian stonework.
“The walls of the prison and courts designed by Thomas Harrison are typical late 18th-century masonry,” he explained. “By the light of my phone I could immediately see that a substantial section of wall ahead was completely different. When I compared the stonework and construction techniques with surviving parts of the Norman castle, it became clear that this wall was medieval.”
The discovery overturns a long-held belief that architect Thomas Harrison had demolished this section of the medieval castle during his extensive redevelopment of the site in the late 18th century.
“The wall is enormous—almost three metres high—which tells us Harrison left far more of the medieval castle intact than previously believed,” said Professor Ainsworth. “It is likely that even more survives beneath the current castle complex and adjoining car park.”
Using high-resolution digital scans, researchers accurately mapped the newly identified structure and compared it with historic plans and maps. The analysis revealed that the wall formed part of a 13th-century bridge crossing the deep defensive ditch surrounding the castle’s inner ward.
The bridge is believed to have been constructed between 1260 and 1280, when a heavily fortified gatehouse replaced an earlier entrance to the castle. That gatehouse was later demolished during Harrison’s redevelopment.
Archaeologists believe the bridge may once have incorporated a drawbridge mechanism, similar to the surviving medieval bridge at Beeston Castle, where visitors can still see the remains of the defensive crossing leading to the twin-towered gatehouse.
The discovery also provides new insight into the evolution of one of England’s most important Norman fortresses. Chester Castle’s original stone gateway, now known as the Agricola Tower, survives nearby and is cared for by English Heritage. The tower houses the Chapel of St Mary de Castro, renowned for its rare 13th-century wall paintings.
The newly discovered remains were documented as part of Digital Dimensions, a collaborative project involving the University of Chester, Cheshire Constabulary, English Heritage, Historic England, SCCS North and the Hartree National Centre for Digital Innovation. The initiative uses advanced digital recording technologies to create detailed 3D models of historic sites while supporting efforts to combat heritage crime.
Project leaders Professor Ainsworth, PC Jonathan Lightfoot, Professor Meggen Gondek and immersive technologies specialist Alex Foster are developing digital methods that can assist police in investigating and preventing the theft, vandalism and damage of historic monuments.
Earlier this year, the partnership also delivered specialist heritage crime training at Chester Castle for 72 police officers from forces across North West England and North Wales, demonstrating how digital technologies and archaeological expertise can help protect vulnerable historic sites.
PC Lightfoot said the discovery highlights the unexpected benefits of proactive digital recording.
“It is amazing that by carrying out detailed surveys of historic buildings, we are able to uncover previously unknown archaeology,” he said. “This discovery means we can now preserve this important part of Chester Castle’s history and continue learning from it for future generations.”
The discovery demonstrates how cutting-edge digital technology is transforming archaeological research, revealing hidden medieval structures while leaving fragile heritage undisturbed.
Header Image : View of the Chester Castle with Agricola Tower – Shutterstock
Sources : University of Chester
