By the beginning of the 5th millennium, cist tombs were being included in earth or stone structures of varying sizes which sealed the entrance to the tomb.
Some of these monuments are small structures (only 10 to 20m long and 1 to 2m high) like the Manio mounds at Carnac, formerly excavated by Péquart, or the Lannec-er-Gadouer mounds at Erdeven, recently studied by S. Cassen.
Others, on the contrary, can be very large, as for instance:
- long barrows, up to 150 m long but relatively low (only 2 to 3 m high) and narrow (Kerlescan at Carnac, Er-Grah at Locmariaquer).
- "Carnacean barrows", which may also be more than 100m long but are wider and often much higher.
The Saint-Michel Tumulus in Carnac, a 120 m long, 50 m wide and 10 m high artificial mound, is the most spectacular barrow of its kind, which also includes Moustoir at Carnac, Tumiac at Arzon, Mané-er-Hroeg and Mané-Lud at Locmariaquer.
Besides their central tombs sealed by the mass of the monument itself, some of these giant barrows (Mané-Lud, St-Michel, Moustoir) also have a passage chamber accessible from the outside at one of their ends. What is then the link between the two types of crypts: Are they contemporary or not? Were their functions complementary?
South-western view of the Saint-Michel Tumulus and its chapel.
Saint-Michel Tumulus of Carnac