Separate layer covering ancient temple (9)
I believe the answer is:
parthenon
'ancient temple' is the definition.
(ancient Greek temple)
'separate layer covering' is the wordplay.
'separate' becomes 'part' (both can mean to split or break apart).
'layer' becomes 'hen' (something which lays - eggs in this case).
'covering' becomes 'on'.
'part'+'hen'+'on'='PARTHENON'
(Other definitions for parthenon that I've seen before include "Ancient temple" , "Tourist attraction of Athens" , "ruined Greek temple" , "Temple of Athene on Acropolis in Athens" , "Temple on the Athenian Acropolis" .)