Well-informed about old city books (10)
I believe the answer is:
literature
'well-informed' is the definition.
The definition and answer are not the same part of speech.
'about old city books' is the wordplay.
'about' is an insertion indicator.
'old city' becomes 'ur' (ancient city state).
'books' becomes 'literate' (I can't explain this - if you can you should believe this answer much more).
'ur' placed within 'literate' is 'LITERATURE'.
Can you help me to learn more?
(Other definitions for literature that I've seen before include "Work by Spenser for instance" , "What author writes" , "writer's work" , "fliers" , "Reading matter" .)