Blowing Up Fort Hill Bastion
As June wore on, Grant pressed the siege with vigor. Johnston tried to help Pemberton, but could not. Grant proceeded to mine under some of the Confederate works to blow them up. One of these, known as Fort Hill Bastion, was in front of McPherson, ad on the afternoon of June 25 it was exploded with terrible effect, making a great breach, at which a fierce struggle ensued.
Benson John Lossing, ed. Harper's Encyclopedia of United States History (vol. 10) (New York, NY: Harper and Brothers, 1912)