Les cultures sont plus vigoureuses et de couleur plus soutenue au-dessus d'anciens fossés qu'il s'agisse d'enclos circulaires de l'âge du Bronze ou de tranchées en zigzag de 1914-18.

Construction projects and their many geometric lines can be a source of confusion. One must beware of lines that appear in parallel to current agricultural fields.
This is less true in winter, partly because the different colors of plowed soil are easy to identify in aerial photographs, and partly because immediate, on-the-ground checks, on bare ground that is readily accessible, eliminate any ambiguity.

In summer or springtime, crop growth anomalies often have the same appearance, whether over contemporary, recent, or very ancient remains. Plants grow greener over filled-in trenches from the Great War than over Bronze Age ditches, but they could very well indicate the location of a manure pile or last year's silos!

In plowed fields in wintertime, on the other hand, differences in soil color allow us to distinguish ditches, even on the ground.

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Tranchée moderne d'une canalisation remblayée aussitôt. Amiens-Nord (Somme).

Entre deux giboulées de mars, l'humidité rémanente souligne l'ancien fossé romain. Érondelle (Somme).