Three anti-tank blocks, part of a World War Two roadblock, stand adjacent to the southeast of the A487 road near the top of Bwlch Llyn Bach. The blocks are made of local stone set in a concrete matrix and each measures about 1.6m x 1.6m x 1.6m. Some 12m to the southwest, a short section of bullhead rail protrudes from the roadside bank. Opposite the blocks two pieces of angle iron, set in concrete, protrude from the northern roadbank. Above these, in line with the three blocks and some 10m from the road edge, is a trench, approximately 10m long, cut along the steep slope and embanked on the side overlooking the road.
Some 85m to the southwest, on the northern side of the road, are the eroded remains of another anti-tank block, constructed in similar style to the other three.
B.A.Malaws, RCAHMW, 12 August 2009.

Surviving Anti-invasion defences (anti-tank cubes) around Fairbourne and Cader Idris: part of Western Command Stop Line No.21

• 270354 Fairbourne Anti-invasion defences (scheduled)
• 800145 Anti-invasion defences, Arthog
• 800146 Anti-invasion defences Llyn Gwernan
• 414156, Anti-invasion defences, Dysyrnant, Happy Valley/Cwm Maethlon
• 270352 Anti-invasion defences, Bwlch Llyn Bach/Cwm Rhwyddfor (scheduled)
• 270350/270351 Anti-invasion defences, Bwlch Oerddrws, east of Cae’r tyddyn (scheduled)

T. Drivr, RCAHMW, 26 July 2023