Nant Ffrancon anti-invasion defences are a Scheduled Ancient Monument dating to the early period of the Second World War. They formed part of Western Command Stop Line No. 23 which ran from Bangor to Porthmadog. The defences are located at the southern end of Nant Ffrancon, where they defend the strategically important Ogwen Pass between Bethesda and Capel Curig. Surviving structures include two pillboxes (NPRN 418763 and NPRN 270452), six spigot mortar emplacements (NPRNs 419778, 270451, 270349, 270449, 419780), three infantry positions and an incomplete alignment of eight anti-tank blocks (NPRN 270450).

Sources include:
Cadw, 2007, Nant Ffrancon Anti-invasion Defences

N Vousden, RCAHMW, 22 January 2014