The most common and most likely answer to this crossword clue is the 6 letter word TUMULI
I've seen this crossword clue in The Daily Telegraph
T
U
M
U
L
I
Buddy explains!

The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TUMULI mean?
TUMULI noun- A mound of earth, especially one placed over a prehistoric tomb; a barrow.