There are almost 500 megalithic sites in Morbihan, but they are unevenly distributed over the area:
The main concentrations lies along the coast between the Blavet estuary and the Rhuys peninsula (including the Morbihan Gulf, the Quiberon peninsula and the Isle of Groix), in particular between the Etel and Auray river estuaries
Another large group of monuments is located on the Landes de Lanvaux, a line of hills between the Claie and Arz valleys, from the Blavet river in the West to the Oust river in the East.
Northern Morbihan has fewer monuments, but they are evenly distributed.
The area between the coast and the Landes de Lanvaux is relatively empty.
Megalithes du Morbihan.
Some megaliths, dolmen (stone passages) and tumuli (dolmen covered by large mounds) are graves and some single standing stones (menhirs) are associated with graves. But the reason for building the long lines of stones (alignments), the stone circles (cromlechs) and many of the menhirs has been lost in the mists of time. Some people think that they are calendars and observatories, so that ancient farmers knew the seasons and when to plant and harvest their crops and the priests could foretell terrifying phenomena such as eclipses of the sun and moon. Alexander Thom, who has surveyed many megaliths in Britain and France, believes that Carnac was a huge lunar observatory. The central of the complex was the huge broken menhir, Le Grand Menhir Brisé, beside the Marchand's Table and Er Grah tumuli at Locmariaquer. The sights to various tumuli and menhirs marked the extreme positions of the moon.
The Megaliths of Carnac
by Vicki Sherwood.
Carnac by The Megalithic Portal.
Many interesting black and white photographs: The Megaliths of Carnac
The Mysteries of Carnac and Atlantis an article by Paul Johnson.