A 13th-century medieval castle long believed to have been demolished has been found intact inside a Victorian building on the Belfield campus of University College Dublin (UCD), according to research by a university academic.

Prof Tadhg O'Keeffe, a specialist in medieval architectural history at the UCD School of Archaeology, identified that the internal walls and structural features of the Norman-era Roebuck Castle remain preserved beneath plaster inside the current 19th-century structure. It had previously been thought that the medieval remains were cleared away when the present building was constructed approximately 150 years ago.

According to Prof O'Keeffe, 18th and 19th-century modernisers constructed the current house around the medieval castle rather than demolishing it. He stated that while the building's exterior appears entirely Victorian, original medieval features survive inside behind plaster finishes, and the current rear courtyard corresponds to the medieval castle courtyard.

Historical records indicate Roebuck Castle was built in the early 13th century in the decades following the Anglo-Norman invasion of Ireland. Its historical occupants included Fromund le Brun, a medieval Lord High Chancellor of Ireland, and the site was reputedly visited by King James II in 1689 before falling into ruin during the 18th century. Prof O'Keeffe noted that the findings allow UCD to claim the oldest standing building structure on any university campus in Ireland.