Appeal upheld by an old church in ancient city (7)
I believe the answer is:
antioch
'ancient city' is the definition.
(ancient Greek city)
'appeal upheld by an old church' is the wordplay.
'appeal' becomes 'it' ('it' can mean something attractive or appealing).
'upheld' says the letters should be written in reverse.
'by' means one lot of letters go next to another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'church' becomes 'ch' (common abbreviation).
'it' reversed gives 'ti'.
'ti' after 'an' is 'anti'.
'anti'+'o'+'ch'='ANTIOCH'
'in' acts as a link.
(Other definitions for antioch that I've seen before include "Place for early Christians" , "Ancient name for Antakya in Turkey" , "early Christian centre" , "Ancient city now Antakya" , "Southern Turkish city" .)