Our fantastic Mr Cope groups Er Grah together with six other big tumuli, calling them the Carnac Grand tumuli, it is a phrase I cannot find elsewhere (granted I haven't tried very hard) so it must be one of his own, possibly.
If it is of the same ilk as Mane er Hroek and the tumulus St Michel then the chamber would have never been able to be entered, they buried the chamber beneath tonnes of Cairn with no passage, so no getting in.
The chamber here, is just visible, the capstone sits proudly just above the cairn. The capstone is again taken from a toppled menhir, but whether it is from Le Grand menhir Brise is a matter for discussion.
There is still no way of getting under the capstone, nor even to try and peak through any gaps as there is no cairn climbing allowed. I know ive sneaked in and there is no one here to tell me off, but some sensitivities remain, and anyway, I'm trying to keep my head down.
The cairn is a massive construction, even now, but originally it would have been much higher, perhaps twice as high as the capstone. Much stone robbing has occurred.
My advice is to get here early, be the first through the door, pay your money, stay a while, and don't be afraid to stray onto the grass. Bloody Frenchies.
Just a few metres away from Table des Marchants is the long mound of tumulus Er Grah – a mighty tapering cairn maybe over 100 metres long. You can't get inside it any more but must walk its length to appreciate it.
This is an academic monograph of explorations of Mesolithic and Neolithic sites. Page 106 discusses excavations at Er-Grah, with emphasis upon the find of two domesticated cattle, which have been radiocarbon dated to sixth or fifth century BC. Indications are that these animals may have been sacrificed at this site.