Many sites were demolished through official clearance schemes or have disappeared as a result of agricultural improvements, forestry plantation and development activity.
Dymchwelwyd llawer o safleoedd drwy gynlluniau clirio swyddogol neu maent wedi diflannu o ganlyniad i welliannau amaethyddol, gweithgarwch plannu coedwigoedd a gweithgarwch datblygu.