Carnac is arguably Europe’s most visually remarkable megalithic site. It is situated near the town of the same name in Brittany. Many will have seen images of the rows of standing stones there, often unaware that there are four main sets of them close to Carnac as well as cromlechs and solitary menhirs, including the largest, Le Grand Menhir Brisé, now broken, but originally 70 ft long and weighing around 300 tons. In their 1978 book [1771.180], Alexander Thom and his son, Archie, in the conclusion to their book, in spite of their extensive studies of the stone rows, agreed that “we do not know what these were for” and although various theories have been proposed since; we still don’t.
Jean Markale presumed that there was a connection between Atlantis and the megalithic standing stones of Carnac in Brittany. Rather than solve these two mysteries, his book, Carnac et L’enigme de L’atlantide (Carnac and the Enigma of Atlantis)  would seem to deepen them.
Helmut Tributsch suggested that the island of Gavrinis near Carnac in Brittany had been the capital of this Atlantean civilisation(a). He dated the destruction of Atlantis to 2200 BC, a date also favoured by Anton Mifsud.
Hans-Pény Hirmenech expressed the wild idea that the rows of standing stones at Carnac marked the tombs of Atlantean soldiers who fought in the Trojan War! Wikipedia notes that “A Christian myth associated with the stones held that they were pagan soldiers in pursuit of Pope Cornelius when he turned them to stone.”(a)
Hank Harrison supports the idea of a megalithic Atlantis with its centre of power, probably located in the Morbihan area of Brittany.
Based on the picture the data present, Schulz Paulsson believes that the megaliths were first constructed by dwellers of northwest France during the second half of the fifth millennium BC.”(b) Mike Parker Pearson, Stonehenge’s leading authority, has endorsed this idea of a French origin for megalith building(c).
>Neil L. Thomas in a 2021 paper(d) has studied three sites near Carnac that hold long rows of standing stones whose purpose was uncertain. Thomas concluded that they had a calendrical function relating to the sun and moon. I cannot help wondering why such extensive and labour intensive structures were needed to achieve this relatively simple objective.<
(d) (99+) Academia.edu *
Hans-Pény Hirmenech was the author of a 1906 book, in French, in which he reviewed possible connections between the Celts, Basques and Atlantis. He claimed that Atlantis had been situated in the North Sea and that Helgoland was a remnant of it.
Hirmenech expressed the wild idea that the rows of standing stones at Carnac marked the tombs of Atlantean soldiers who fought in the Trojan War!
Hirmenech was a founding member of la Société Préhistorique Française (The Prehistoric Society of France)(a).
[I’m indebted to Stelios Pavlou for some details above.]