Thirlwall Castle is a picturesque ruin set on a spur overlooking the Tipault Burn in the outstanding landscape of the Northumberland National Park. Close to Hadrian’s Wall, Britain’s most important Roman monument, the castle was constructed in the fourteenth century by John de Thirlwall using stones ‘robbed’ from the Roman wall. In this way the castle provides a physical link with the two most important historical periods in the North of England: the Roman occupation (c.54-409) and the Border wars between England and Scotland (c.1296-1545). Thirlwall is a significant part of Northumberland’s cultural heritage, within the Hadrian’s Wall UNESCO World Heritage Site and on the Pennine Way and Hadrian’s Wall long distance walking routes. The ruin is also ecologically significant as a wildlife habitat with a colony of Swifts and in a geological Site of Special Scientific Interest.
Disused by the mid C17, the castle fell into ruin and was subjected to stone robbing, erosion by the elements and the effects of uncontrolled vegetation. Its survival was due to the massive construction and use of the Roman stones, which have long ‘tails’ embedded up to 400mm (1’4”) into the wall core. Nevertheless, by the 1990s it was in a dangerous state and major conservation works were urgently needed to prevent further collapses. We took the lead in assessing its condition, researching, designing and managing the stabilisation and consolidation project , A key feature of our approach was the integration of natural and built heritage conservation. The project included restoring a lost window opening and sections of walling to provide structural supports, grouting and repointing using lime mortars, and innovative ‘soft capping’ wallhead treatment which re-used the original vegetation to preserve the natural appearance of the monument.
The castle is visited by many holiday-makers, school children and walkers, and we have maintained our involvement over a number of years by returning to carry out condition inspections and advise on maintenance. The project won a Civic Trust Commendation and the soft capping work has contributed to research on the subject: see article.