Ancient Aegean region (5)
I believe the answer is:
'ancient aegean region' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ionia that I've seen before include "East coast of the Aegean in Classical times" , "ancient region of Eastern Mediterranean" , "Classical Aegean region" , "Ancient area" , "Ancient Greek region" .)