Rocky Inca road north is harsh (9)
I believe the answer is:
draconian
'harsh' is the definition.
(thesaurus)
'rocky inca road north' is the wordplay.
'rocky' indicates an anagram.
'north' becomes 'n' ('N' can be a synonym of 'north').
'inca'+'road'='incaroad'
'incaroad' with letters rearranged gives 'draconia'.
'draconia'+'n'='DRACONIAN'
'is' is the link.
(Other definitions for draconian that I've seen before include "Very strict" , "Cruel" , "Incan road (anag) - extremely harsh" , "Savage" , "Excessively severe" .)