Ancient burial mound (7)
I believe the answer is:
tumulus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ancient burial mound</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 tumulus that I've seen before include "Ancient barrow" , "burial-place" , "Ancient burial mound" .)