angles appearance backdrop background backgrounds barrier blocks colors colours constructed contrast contrasts cracks discoloration fitted foundation foundational growth height high large limestone linear lines mortar moss old perspective perspectives plants retaining retaining-wall secure security solid stone stones stonework strength strong surface surfaces texture textures variations variety wall walled well-built architecture calm dam Elan Valley hill lake mountain power reflection reservoir retain wales water welsh arches hold landmark landscape tower abstract bolders boulders cemented coated concrete cover covered erosion-prevention random randomly-coursed Rendered retaining-rocks rock rocks rocky rough rugged slope sloping stone-walled uneven hills buttresses road