Invader is new, Roman-style (6)
I believe the answer is:
norman
'invader' is the definition.
(as in the Norman Conquest of 1066)
'new roman-style' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'style' is an anagram indicator (style can mean to shape or design).
'roman' is an anagram of 'orman'.
'n'+'orman'='NORMAN'
'is' is the link.
(Other definitions for norman that I've seen before include "Ten sixty six invader" , "-- Wisdom, comedian" , "12th century invasion of Ireland" , "British comedian, once a cult figure in Albania, d. 2010" , "Australian golfer" .)