Royal Marine crosses Roman road in high spirits (8)

I believe the answer is:

jovially

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'royal marine crosses roman road in high spirits' is the definition.
I can't tell whether this defines the answer.

'royal marine crosses roman road' is the wordplay.
'royal marine' becomes 'jolly'.
'crosses' indicates putting letters inside.
'roman road' becomes 'via' (I've seen this before).
'jolly' placed around 'via' is 'JOVIALLY'.

Can you help me to learn more?

(Other definitions for jovially that I've seen before include "In a cheerful and friendly manner" , "In a jolly and friendly manner" .)

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