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Origin and history

Er Lannic's cromlech is a double megalithic enclosure located on the island of Er Lannic in Arzon, Morbihan. Discovered in 1866 by Gustave de Closmadeuc, the site consists of two hemicycles of raised stones, one of which was later identified in 1872 during a great tide. These structures, partially submerged today, were built in Neolithic, when the sea level was 5 metres below today's. Ranked a historic monument in 1889, the site was searched and restored, notably by Zacharie Le Rouzic and Saint-Just Péquart between 1923 and 1926.

The north hemicycle, almost rectangular, measures 52 m by 50 m and opens southeast, while the south hemicycle, more regular with a diameter of 60 m, opens east. The local granulite and migmatite stones reach up to 8.20 m for the large broken menhir. Four slabs of the north enclosure bear engravings, including axes and cupules, perhaps evoking symbolic or astronomical representations. Differences between the two enclosures suggest distinct construction periods, about -3,500 B.C.

Archaeological excavations revealed a rich neolithic furniture: incinerated bones, flint tools (arrow tips, scrapers, axes), and hunting ceramics, including burning-parfum vases. These discoveries, preserved at the Museum of Prehistory of Carnac, indicate an occupation of the site around -4,000 B.C., combining functions of size workshop, habitat, and ritual center. The gradual immersion of the site results from the postglacial isostatic rebound, changing the landscape since its construction.

Subsequent studies, such as those carried out in 1991-1992 by the Archeo Douar Mor association, cleared the site and refined its underwater topography. Isolated menhirs, located near the east and west shores, add to the complexity of the site, whose exact articulation with the enclosures remains enigmatic. Er Lannic's cromlech thus illustrates the neolithic practices of symbolic management of space and resources, in a context of rising waters.

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