Port city of ancient Rome (5)
I believe the answer is:
ostia
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">port city of ancient rome</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ostia that I've seen before include "ruined port" , "openings in Rome" , "port in former times" , "town near Rome" , "Small openings" .)