The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 5: Forts and Artillery.
Francis Trevelyan Miller, Ed.

Previous to the movement of Lee's army, every effort had been made to advance the work of construction, so that the city could be defended easily during the absence of the main body, and by the time Lee invaded Maryland, the second line of outer works had been almost completed around the city at a distance of a mile to two miles from the first series of forts.

Outside of this continuous line were erected some small detached works, which formed the basis for a third line, built in 1864, not so complete as the second, but covering all of the principal approaches at a still greater distance from the city.

In October, 1862, during the absence of the Army of Northern Virginia from the immediate vicinity of Richmond, there were about two thousand troops assigned to the defenses, and these were engaged in keeping the works at their maximum efficiency, and in ensuring protection to the capital against small Federal raiding parties. The batteries at Chaffin's and Drewry's bluffs were held in sufficient force to prevent the ascent of the river by Union gunboats.

The works of the third line which were first built could not have much effect on a hostile army's advance, but as long as there was an opportunity of improving the strength of the general scheme of fortifications, work was continued. In some cases those of the third line at first were without proper protection on the flanks, and as it was useless to try to hold works that only jeopardized the safety of their defenders, General Hill, in July, 1863, reported that the entrenchments in that line on the west of the Brook turnpike, overlooking Brook Run, a stream flowing into the Chickahominy near Meadow Bridge, were not constructed so as to cover all the ground necessary; and that the infantry parapets were not strong enough.

At his suggestion, all the troops available were put to work at once by the chief engineer, Colonel J. F. Gilmer, all obstructions removed from the front of the works, the parapets of some of the heavier batteries made stronger, and the lines of infantry cover connecting the redoubts improved.