Altar he'd destroyed going after Catholic Church (9)
I believe the answer is:
cathedral
'church' is the definition.
(cathedral is a kind of church)
'altar he'd destroyed going after catholic' is the wordplay.
'destroyed' indicates an anagram.
'going after' means one lot of letters go next to another.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'altar'+'hed'='altarhed'
'altarhed' anagrammed gives 'athedral'.
'athedral' put after 'c' is 'CATHEDRAL'.
(Other definitions for cathedral that I've seen before include "See building" , "Principal church of see" , "Place of worship" , "Head church of diocese" , "City's main church" .)