Sentence:  We did not catch them napping, but found a well-entrenched <WSD>battle line</WSD> confronting us. 
Meaning of the word marked with <WSD> tags:  The notional line on either side of which opposing forces are arrayed, and at which they meet in battle; a fortified line, short of the line where battle is expected, and behind which forces are arrayed; a forward line of infantry or other force, prepared for battle.