A blockade is the strategic placement of a piece—typically a knight—directly in front of an enemy pawn to prevent its advance. The concept was systematised by Aron Nimzowitsch in his influential work My System (1925). Nimzowitsch argued that the ideal blockader is a knight, as it is not impeded by the pawn it blocks and can exert influence in multiple directions from its blockading square. Blockading a passed pawn or an isolated pawn is a fundamental positional technique.