Pack forcibly split defence (7)

I believe the answer is:

rampart

I'm a little stuck... Click here to teach me more about this clue!

'defence' is the definition.
(rampart is a kind of defence)

'pack forcibly split' is the wordplay.
'pack' becomes 'ram' (synonyms).
'forcibly split' becomes 'part' (synonyms. I am not sure about the 'forcibly' bit.).
'ram'+'part'='RAMPART'

Can you help me to learn more?

(Other definitions for rampart that I've seen before include "means of defence" , "Defensive wall or mound" , "Bulwark, wall" , "Battlement, fortification" , "Military protection" .)

I've seen this clue in The Times and The Sun.

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