Ancient city vandalised by thanes! (6)

I believe the answer is:

athens

I'm a little stuck... Click here to teach me more about this clue!

'ancient city' is the definition.
'athens' can be an answer for 'city' (Athens is an example). I am not certain of the 'ancient' bit.

'vandalised by thanes' is the wordplay.
'thanes' anagrams to 'ATHENS'.
But, I am not clear how this is indicated.

Can you help me to learn more?

(Other definitions for athens that I've seen before include "Hasten to the Hellenic city" , "Site of the Parthenon" , "Plato's birthplace" , "Greek capital" , "Tan she got in Greece" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.