RomanArmyTalk

What was the role of the garrison s demoralization in the falling of fortresses in ancient warfare? Which factor played crucial role – the quality of fortification or the morale of troops which defended here?

I'd say a mix of both - morale would not be good when defences are in a bad condition.
But morale would be a major factor - fortresses in good condition can fall when morale is bad, we have many examples of that.