Enemy of ancient Athens (6)
I believe the answer is:
sparta
'enemy of ancient athens' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sparta that I've seen before include "Old Greek city state, famous for its citizens' austere lifestyle" , "it was a hard place" , "Laconic state" , "Where to find ancient Greek" , "Ancient kingdom renowned for asceticism" .)