A decorative scheme applied to the internal gable wall at the ‘high’ end of the hall of Oakham Castle, in Rutland, has been the subject of recent investigation, with the removal of later over-painting. Analysis indicates that the scheme is original Romanesque work dating from the 1180s, an exceptional survival for a secular building. Very unusually, the decoration was produced with self-coloured plaster rather than paint. The scheme, of which quite extensive sections survive, consisted of a large semi-circular arch with voussoirs (similar to the hall’s main stone arcade), and a lattice pattern simulating opus reticulatum in the tympanum below. The pattern was created by laying white lime strips over a buff-coloured plaster background. The only comparable example yet identified – at Chepstow Castle, in Monmouthshire – is on a smaller scale and a century earlier. The scheme seems to have survived because the interior of the hall has been little disturbed, with a tradition since the fifteenth century of displaying outsized horseshoes on the walls.