The outer slope of a defensive or fortified ditch(noun)
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Use "counterscarp" in a sentence
"The counterscarp is substantially built of plank, and spread with turf."
"Why, the old Peer, pox of his tough constitution, (for that malady would have helped him on,) has made shift by fire and brimstone, and the devil knows what, to force the gout to quit the counterscarp of his stomach, just as it had collected all its strength, in order to storm the citadel of his heart."
"We passed the demilune, we passed the culverin, bayoneting the artillerymen at their guns; we advanced across the two tremendous demilunes which flank the counterscarp, and prepared for the final spring upon the citadel."