A single protohistoric circle (the white line marks the path of a recent drainage installation). Vitry-en-Artois (Pas-de-Calais).
Double circle at Cardonnette (Somme).
Large Bronze Age sanctuary with three concentric circles at Fouilloy (Somme) at "Champ-Saint-Martin".
Aerial photography has allowed us to discover thousands of monuments that are easily identified by their circular ditches, which appear either singly or in concentric rings. Sometimes the circles are isolated, but they are more often grouped, forming necropoli and places of worship.
Some circles have interruptions and secant areas, like at Londinières (Seine-Maritime). The circles, made from posts of wood or stone (Woodhenge or Stonehenge) are mainly known in Great Britain starting in the Neolithic.
The large monuments with three concentric circles at Fréthun (Pas-de-Calais) and Noyelles-sur-Mer (Somme) have a long funerary tradition, since sometimes Gallic and Merovingian cemeteries were established at the same spot (Blancquaert et alii 1992).