Adam Badeau, Military history of Ulysses S. Grant from April 1861 to April 1865. Volume 2

[6] with occasional detached works, or keeps, sometimes redoubts, to which the troops might retire in the event of the principal line being carried; while in front of all were the rifle-pits for the pickets, these also connected by a parapet affording good cover, and forming in fact a field fortification in all but relief; they were even furnished at many points with rude but effective obstructions in the shape of slashed timber, which made a sort of abatis or fraise. These obstructions, however, were sometimes carried away for fuel by the troops on either side, under the tacit understanding so often witnessed between advanced forces in the field.

Besides the works in front of Petersburg, there were two more lines between that city and Richmond, upon which the rebel army might fall back, if those south of the Appomattox should be forced; but the position at Petersburg was the important one, as any line nearer Richmond would not enable Lee to keep open his communications by the Southside railroad. The whole series of works around Petersburg thus became a part of the defences of Richmond; and, confronted from the middle of June by the entire army of the Potomac and a part of Butler's force, it acquired that character which the presence of a large body of defenders alone made practicable. Forts with very strong relief; a connecting parapet assuming the profile of regular field works, and protected in front by two and even three rows of entanglements; the whole line well flanked, and its approaches everywhere swept by artillery—these constituted a position, which, when held by only one rank of good troops with breech-loading