Barnenez
Plouezoc'h, France · built -4500
The Cairn of Barnenez (also: Barnenez Tumulus, Barnenez Mound, in Breton Karn Barnenez, in Cairn de Barnenez or Tumulus de Barnenez) is a Neolithic monument located near Plouezoc'h, on the Kernéléhen peninsula in northern Finistère, Brittany, France. It dates to the early Neolithic, around 4000 BC. Along with the Tumulus of Bougon and Locmariaquer megaliths, also located in Great West France, it is one of the earliest megalithic monuments in Europe and one of the oldest man-made structures in the world. It is also remarkable for the presence of megalithic art.
Monument data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).