Promotion of article supporting ancient city in EU country (11)

'promotion' is the definition.
('furtherance' can be a synonym of 'promotion')

'article supporting ancient city in eu country' is the wordplay.
'article' becomes 'the' (the 'definite article' part of speech**).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'ancient city' becomes 'ur'.
'in' means one lot of letters goes inside another.
'eu country' becomes 'france'.
'the' put after 'ur' is 'urthe'.
'urthe' put into 'france' is 'FURTHERANCE'.

'of' is the link.