Historic battle of marginal prominence (8)
I believe the answer is:
edgehill
'historic battle' is the definition.
'edgehill' can be an answer for 'battle' (I've seen this before). I'm unsure of the 'historic' bit.
'marginal prominence' is the wordplay.
'marginal' becomes 'edge' (synonyms).
'prominence' becomes 'hill' (I can't explain this - if you can you should give a lot more credence to this answer).
'edge'+'hill'='EDGEHILL'
'of' is the link.
Can you help me to learn more?
(Other definitions for edgehill that I've seen before include "First battle of the Civil War, 1642" , "battleground" , "Sixteen forty two Civil War battle" , "Battle of the English Civil War" , "where battle was fought" .)