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 shadow of a mighty Negro past flits through the tale of Ethiopia the shadowy and of the Egypt the Sphinx. Throughout history, the powers of single blacks flash here and there like falling stars, and die sometimes before the world has rightly gauged their brightness.”
—W.E.B. (William Edward Burghardt)
“Now only a dent in the earth marks the site of these dwellings, with buried cellar stones, and strawberries, raspberries, thimble-berries, hazel-bushes, and sumachs growing in the sunny sward there.... These cellar dents, like deserted fox burrows, old holes, are all that is left where once were the stir and bustle of human life, and “fate, free will, foreknowledge absolute,” in some form and dialect or other were by turns discussed.”
—Henry David Thoreau (1817–1862)