BREACH, in Fortification, is a gap or opening made in any part of the works of a 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. A practicable breach is that where men may mount and effect a lodgment, and it ought to be fifteen or twenty fathoms wide. The besiegers sometimes make their way to it by covering 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 cover or protection, and to trust for success to their own daring and perseverance.