Mark moved dean to a portico (9)
I believe the answer is:
colonnade
'to a portico' is the definition.
(I've seen this in another clue)
'mark moved dean' is the wordplay.
'mark' becomes 'colon' (colon is a kind of punctuation mark).
'moved' is an anagram indicator.
'dean' is an anagram of 'nade'.
'colon'+'nade'='COLONNADE'
(Other definitions for colonnade that I've seen before include "Row of columns supporting a roof" , "Arcade" , "Row of evenly spaced pillars" , "supporters in a row" , "Collection of columns" .)