Dear Alexandra, I know nothing similar to your case, but I've seen several examples of physical limits made just under the tumulus walls around some dolmens in France, during excavations. They look like a small dug trough or a line of small stones and they show the original drawing on the ground made by the Neolithic architect planning to build his monument. But in your case, the feature is different.

Thanks Bertrand for your answer. 

Do you know were the example that you refer was publish?

Best wishes

Dear Prof. Figueiredo, 

I specialize in the Early Byzantine period and therefore I am not so familiar with the type of dolmen you describe in your article. I'm sorry I can be of no assistance.

All the best,

Karni 

Thanks Karmi for trying to help. If you ear about something similiar please let me know.

Best wishes

Dear Alexandra,

one of the examples has been published here:

https://www.researchgate.net/publication/262198194_Le_vrai-faux_dolmen_de_Vialamontels_une_histoire_edifiante?ev=prf_pub

See figure 4 "rainure dans le substrat".

Best wishes,

Bertrand

Chapter Le vrai-faux dolmen de Vialamontels : une histoire... édifiante

Thanks Bertrand, I will see it with all atention.

best wishes, once again