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Origin and history

The cairn of Carn Island, located on an island accessible at low tide near Ploudalmezeau (Finistère), is a major megalithic ensemble of Neolithic. Built around 4200 B.C. for its first two dolmens and 3600 B.C. for the third, it consists of a trapezoidal primary cairn housing three corridor dolmens, later covered by a circular cairn "discontinued" without entry. This site revolutionized archaeology: in 1959, the 14 carbon dating of the central dolmen, revealing an antiquity of 1,600 years higher than the oldest Egyptian pyramid, changed the knowledge of European megalithism.

Originally, the primary cairn, estimated at 600 m3, dominated a continental landscape, the sea level being 8.80 m lower. Its three dolmens, aligned from southwest to northeast, have distinct architectures: corbelled vaults, narrow corridors, and for the north dolmen, a division into two sub-chambers. The furniture discovered (shale pearls, pottery, flint tools) attests to a funeral and ritual use over more than a millennium, with late inputs around 3000 BC.

In the final Neolithic, the primary cairn was deliberately buried under a circular cairn of 30 m in diameter, without access, constituting a "mass of prohibition" unique in Brittany. The excavations carried out by Pierre-Roland Giot from 1954 to 1972 allowed its partial restoration, after the destruction suffered during the Second World War, when the Germans installed a casemate there. Ranked a historic monument in 1955, the site illustrates the evolution of funeral practices and architectural ingenuity of neolithic societies.

The secondary cairn, initially a dome of pebbles and granite fragments, was partially reconstituted to reveal the front of the primary cairn. Its wall, exceptionally well preserved, is composed of superimposed granite pads, surmounted by a black earth chape. Today, the whole reaches a height of 18 m, with a south appendix masking the remains of the casemate. The dolmens, accessible by narrow entrances, offer rare evidence of dry stone construction techniques and beliefs of the time.

The excavations also revealed a variety of furniture, including pumice stone objects, arrows, and a polished axe, reflecting distant exchanges and an organized society. The more recent north dolmen is distinguished by its furniture after a millennium, suggesting a prolonged reuse of the site. The consolidation work (1967–72) preserved the corbelling vaults and the trimmings, although some reconstitutions, such as the north dolmen, remained hypothetical.

A symbol of Breton megalithic heritage, the Carn Island cairn embodies both a place of memory and a scientific milestone. Its discovery marked a turning point in the understanding of Neolithic, while its preservation bears witness to efforts to protect an older legacy of over 6,000 years. Owned by the Finistère department, it remains a key site for the study of funeral practices and prehistoric architecture in Europe.

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