A line of anti-tank blocks is located in the valley of Nant Tywyni, a tributary of the upper Tawe, just below the A4067 road to the south of Cray.
There are 15 blocks forming a sinuous line along the east bank of the stream, clearly visible from the roadside verge. The blocks can be dated on the basis of their orientation and alignment (diagonally set with corners of adjacent blocks facing each other) to late 1940 or early 1941. The blocks are faced in dressed stone but will have a concrete core reinforced with iron. The tops of the stones are capped in light vegetation where vertical stones were set into the blocks to encourage natural growth as camouflage. Stream erosion has caused two of the blocks to topple over.
These anti-invasion defences will have been accompanied by other defensive features as yet unrecorded.

David Leighton, RCAHMW, 23 June 2011