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:
“I was the shadow of the waxwing slain
By the false azure in the windowpane;
I was the smudge of ashen fluff—and I
Lived on, flew on, in the reflected sky.”
—Vladimir Nabokov (1899–1977)
“I am glad I made the late race. It gave me a hearing on the great and durable question of the age, which I could have had in no other way; and though I now sink out of view, and shall be forgotten, I believe I have made some marks which will tell for the cause of civil liberty long after I am gone.”
—Abraham Lincoln (1809–1865)