Antonine Wall, Twechar
Antonine Wall near Bar Hill Roman Fort, near Cumbernauld.
The high tide mark of Roman expansion northwards into Britain, the turf wall is less famous than its older stone-built brother. Clearly a wall too far, it was soon abandoned and the frontier re-established at Hadrian's wall further South.
This cameraphone shot doesn't give much impression of the scale, but after 1800 years it is still enormously impressive. Or impressively enormous.