Parchmarks recorded during Royal Commission aerial reconnaissance on 22nd July 2013 document the concentric circles of square and circular concrete footings which once provided the base and anchoring point for a Second World War barrage balloon. A postcard in a private collection, showing an aerial view of the castle taken late in the war, shows the platform in place with accompanying huts at the northern end of the castle interior sited against the base of the earthen rampart. Plate V.A in Jarrett's 1969 'The Roman Frontier in Wales' (University of Wales Press) shows Cardiff Castle in an aerial view sourced from Country Life. This view also records the circular parchmarks of the barrage balloon site in the same position. The subsurface remains of this emplacement were recorded in a 2001 Stratascan geophysical survey of the castle interior.

T. Driver, RCAHMW, 2013, with information kindly provided by Dr Peter Webster.