Preserved from civilisation once (5)
I believe the answer is:
incan
This might be a double definition.
'preserved' is the first definition.
Both the definition and answer are adjectives.
Maybe there's an association between them I don't understand?
'from civilisation once' is the second definition.
(from the Inca civilisation)
(Other definitions for incan that I've seen before include "Of a native Peruvian" , "Relating to ancient South Americans" , "Old Peruvian" , "Relating to pre-conquest Peruvians" , "like former S American civilisation" .)