BREACH, in Fortification, is a gap made in any part of the works of a town or fortress by the cannon or mines of the besiegers, with a view to an assault upon the place. To render the attack more difficult, the besieged sow the breach with crow-feet, stop it up with chevaux de frise, or retrench it by cutting traverses within. The besiegers sometimes protect themselves with gabions, earth-bags, and the like; but in our army the practice has always been for storming parties to advance to the breach without any such protection, and to trust for success to their own daring.