Left a stone erected topped with huge stone (8)

I believe the answer is:

megalith

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'huge stone' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for megalith that I've seen before include "Huge ancient monument stone" , "Huge stone used in prehistoric monuments" , "Upright (prehistoric) stone" , "Large stone in a prehistoric monument" .)

I've seen this clue in The Telegraph.

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