The tacchi are remnants of a Mesozoic limestone cover that was once continuous and which erosion reduced to isolated blocks. The contrast between pale limestone and the darker schists beneath is visible to the naked eye along many inland roads.
Very concrete things follow from that structure: where springs emerge, where caves open, where people climb, and why villages often sit at the foot of the walls rather than on top of them.
A note on the photograph: the image on this page shows Perda 'e Liana, one single tacco, and not the whole territory of the Tacchi of Ogliastra, which comprises distinct reliefs across several municipalities.
