Back hawk-headed god seen in Athenian market (5)
I believe the answer is:
agora
'athenian market' is the definition.
(I've seen this in another clue)
'back hawk-headed god' is the wordplay.
'back' becomes 'ago' ('years back' means 'years ago').
'hawk-headed god' becomes 'ra' (Egyptian god).
'ago'+'ra'='AGORA'
'seen in' acts as a link.
(Other definitions for agora that I've seen before include "where Greek characters assembled" , "Foreign brass" , "Marketplace in ancient Greece" , "Meeting-place in Athens" , "11 [LOLLY] to Ben-Gurion" .)