Roadside markers transforming solemn site (10)

I believe the answer is:

milestones

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'roadside markers' is the definition.
'milestones' can be an answer for 'markers' (milestone is a kind of marker). I'm not certain of the 'roadside' bit.

'transforming solemn site' is the wordplay.
'transforming' indicates anagramming the letters (I've seen this in other clues).
'solemn'+'site'='solemnsite'
'solemnsite' is an anagram of 'MILESTONES'.

Can you help me to learn more?

I've seen this clue in The Times.

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