To march in the opposite direction; in military terms, to reverse the direction of a marching formation without changing the front.
From 'counter-' (against) plus 'march' (from Old French 'marche', a boundary or military walk, possibly related to Proto-Germanic 'markōn'). Medieval military drilling term.
Military drill teams still practice countermarching—it's a precise maneuver where soldiers reverse direction in formation. Watching a perfect countermarch looks like magic, but it takes weeks of practice!
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