A close-up of the vertical slab set into
the outer retaining wall.
One of only two such slabs in the exterior walling, choice of location for this
feature is a mystery. The other slab is associated with the upper chamber
entrance passage and delimits a curious recess in its western wall. Upright
slabs are important features of the cairn's internal structure and
serve to define the internal spaces and compartments, but the external slab
above has no readily apparent function.