Many Welsh hills (over 600) are still crowned with massive, weather-beaten earth and stone enclosures, major feats of engineering all dug by hand.
Mae llawer o fryniau Cymru (dros 600) wedi’u coroni o hyd â llociau enfawr, hindreuliedig o bridd a cherrig, a oedd yn gryn orchestion peirianneg, a’r cyfan wedi’i gloddio â llaw.