We hear the stronghold went into action (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
fought
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for fought that I've seen before include "Battled" , "Exchanged blows" , "Made a strenuous or laboured effort" , "Through the courts opposed" , "Opposed, struggled" .)