And Gavrinis too

Another of the great cairns or burial mounds in Brittany is at Gavrinis -- on an island not far from Carnac.  It's also very impressive, with a megalithic slab structure in the passages and the main chamber.

Again, the date is Neolithic, but it seems that the builders here (a few centuries later than those who built Barnenez, Ile Carn and Guennoc) did not use corbelling techniques -- and they may therefore have been a bit less sophisticated as builders.  But the structure is still a sort of stepped pyramid.