Ancient besieged city (4)
I believe the answer is:
troy
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ancient besieged city</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for troy that I've seen before include "System of weights introduced by French" , "Wooden horse siege city" , "See 7" , "City impacted by long-term investment" , "part of Asia Minor" .)