Ancient Roman ship (7)
I believe the answer is:
trireme
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ancient roman ship</span>' is the definition.<br/ >'<span class="explanation-format__answer">trireme</span>' can be an answer for '<span class="explanation-format__original">ship</span>' <span class="explanation-format__explanation">(I've seen this before)</span>. I also know that both 'ancient' and 'roman' relate to this answer.<br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for trireme that I've seen before include "Ancient Greek or Roman war galley" , "Ancient galley with three tiers of oars on each side" , "Ancient rowed ship" , "Roman/Greek galley" , "Ancient vessel with three banks of oars on each side" .)