Overshadowed by Snowdonia to the north and the Brecon Beacons to the south, mid Wales is something of a 'green desert'. Shrouded by Celtic mists, it baffled the advance of the English invaders, thus preserving the Welsh language in the west of Wales. The tranquil borderland of the Marches, offers a varied landscape truncated by rivers meandering to lowland plains. Limestone to the west and north of the old red sandstone of the Hereford Plain has given rise to exceptionally attractive hilly country with delightful, narrow valleys.