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.