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:
“We saw one schoolhouse in our walk, and listened to the sounds which issued from it; but it appeared like a place where the process, not of enlightening, but of obfuscating the mind was going on, and the pupils received only so much light as could penetrate the shadow of the Catholic Church.”
—Henry David Thoreau (1817–1862)
“I regard almost all quarrels of princes on the same footing, and I see nothing that marks man’s unreason so positively as war. Indeed, what folly to kill one another for interests often imaginary, and always for the pleasure of persons who do not think themselves even obliged to those who sacrifice themselves for them!”
—Mary Wortley, Lady Montagu (1689–1762)