In most places,where the Wall descends river terraces,the Wall has been destroyed,but here at Willowford,the Wall survives.This image,is looking down that section of Wall across the Irthing Valley towards The Roman Bridge abutment.The flag stones on the rhs of the picture,are modern steps put in to assist tourists to descend the river terrace.
see http://www.hadrianswallcountry.org/wall.asp