Contrary to the common belief, megaliths have not gone unchanged through the centuries.
Like all buildings, they are indissociable from the lives of the men who used them and adapted them to their needs at all times:
the Petit-Mont was turned into a Gallo-Roman sanctuary, the Cruz-Moquen dolmen at Carnac was christianised, others have been used as quarries since ancient times (the Table-des-Marchands) and right until the present day (the Petit-Menec alignments, or the Rondossec dolmens).
These monuments were transformed and adapted by the Neolithic inhabitants while they were still in use, through:
- Accretion of cairns or mounds, with two major examples: the Petit-Mont cairns and the Er-Grah tumulus at Locmariaquer.
- Extension or change in the plan of some groups of menhirs, as the Kermario alignments: the Manio mound "spanned" by what is probably an extension of the alignments, the out of line menhirs near the "Petite-métairie", testifying to a possible older period.
- Changes in the structure of some monuments (the sandstone stele at Locmariaquer incoporated into the Table-des-Marchands tomb or the closure of the access to Gavrinis).
- Breaking up monuments with or without reuse of the elements in new buildings, for instance: the breaking up of the alignment related to Grand-Menhir at Locmariaquer with possible reuse of the blocks in other monuments and reuse of already decorated slabs to build Gavrinis.
The Cruz-Moquen christianised dolmen at Carnac, from an old photograph.
At Kermario, several menhirs are transversal to the lines and could be the remains of structures older than the present alignments.