Shadow marks are a form of archaeological feature visible from the air. Unlike cropmarks, frost marks and soil marks they require upstanding features to work and are therefore more commonly seen in the context of extant sites rather than previously undiscovered buried ones.
They are caused by the differences in height on the ground produced by archaeological remains. In the case of ancient, eroded earthworks these differences are often small and they are most apparent when viewed from the air, when the sun is low in the sky. This causes long shadows to be cast by the higher features, which are illuminated from one side by the sun, with dark shadows marking hollows and depressions.
Shadow marks are best viewed obliquely rather than from directly above in order to emphasise the effect of the shadows.
Famous quotes containing the words shadow and/or marks:
“The best history is but like the art of Rembrandt; it casts a vivid light on certain selected causes, on those which were best and greatest; it leaves all the rest in shadow and unseen.”
—Walter Bagehot (1826–1877)
“... my aim is now, as it has been for the past ten years, to make myself a true woman, one worthy of the name, and one who will unshrinkingly follow the path which God marks out, one whose aim is to do all of the good she can in the world and not be one of the delicate little dolls or the silly fools who make up the bulk of American women, slaves to society and fashion.”
—Ellen Henrietta Swallow Richards (1842–1911)