Sentence:  While tradition and speculation has it that <WSD>murder holes</WSD> were commonly used to throw stones and other heavy missiles onto the heads of unsuspecting besiegers, they quite likely originated as devices that allowed defenders to quench the flames of an enemy's fire burning the timber defenses situated within the passage. 
Meaning of the word marked with <WSD> tags:  A slit or hole above the entrance to a fortification, thought to provide access for defenders to kill invaders.