The mound covers a single rectangular (nearly square) slab-built burial chamber, located at the centre of the mound and measuring about 2.5m across. The chamber is built of about 50 carefully placed slabs. The biggest of these is the ceiling slab which weighs nearly 17 tons. Such simple dolmen-type chambers, reached by passages, were very common in Brittany between 4500 and 3000 BC. At the same time, similar monuments were constructed in Normandy and Poitou, in Ireland, Britain, and the Iberian Peninsula.
