The huge slab covering the chamber (7m long, 4m wide and up to 0.8m thick) is made up of allochtonous orthogneiss.
The fracture above the passage had already been noticed by archaeologists in 1811 (and probably even by Marquis de Robien in the 18th century).
In 1983, it was shown to be "connected" with the cover of the Gavrinis chamber, 5km away beyond the Auray river.
The decorations found on these two stones fit perfectly and the third part of this giant monolith might be the cover of the Er-Grah burial-chamber, thus leading to the hypothesis of a "second grand menhir", which would have been 14m long, and displayed an elaborate superimposition of figures pecked in the rock.
Moving this 65 ton stele to Locmariaquer (probably to erect it next to the Grand-Menhir) was not likely to be a problem for men who had been capable of moving the 280 ton Grand-Menhir.
Pulling it down was probably part of the general process of breaking-up the alignment. As for the cutting up and reuse of the fragments, it was either simply a desire to reuse the pieces or a deliberate attempt to incorporate into all monuments involved some of the significance of this extraordinary stone.
The fracture of the orthogneiss slab over the passage has been revealed during excavation.
Reconstructing the large ornate stele, the lower half of which makes up the ceiling of the Table-des-marchands