position of Upton's and Munson's Hills, and the works of Fort Ramsay, Buffalo, &c., were commenced and speedily finished.
In September the fortification of the heights over the Eastern Branch was commenced.
During the subsequent months of the autumn and winter the engineers, assisted by large details of troops and also by large gangs of hired laborers, were busily engaged in completing the system, which, as you will observe, now extended from a point below Hunting Creek, near Alexandria, to the Chain Bridge, thence from the Potomac to the Eastern Branch near Bladensburg, and thence along the heights south of the Eastern Branch to a point nearly opposite Alexandria, making a total development of 33 miles.
I refrain from making here an exact enumeration or a minute description of the works. A report to the Chief Engineer, U. S. Army, made by me December 10, 1861, in compliance with a resolution of the House of Representatives (a copy of which was furnished to General McClellan), will furnish all such details. They should not be made public. I incorporate in this report the following extract:
The aggregate perimeter of all the works is about 15,500 yards, or nearly 9 miles (including the stockaded gorges, which, however, form a small proportion of the whole), requiring computed according to the rule adopted for the lines of Torres Vedras, 22,674 men (about) for garrison.
The number of guns (most of which are actually mounted) is about 480, requiring about 7,200 men to furnish three reliefs of gunners. The permanent garrisons need consist of only these gunners, and even in case of attack it will seldom be necessary to keep full garrison in all the works.
The total garrisons for all the works (152 in number) of Torres Vedras amounted to 34,125 men, and as the total perimeters are nearly proportional to the total garrisons, it appears that the lines about Washington in love a magnitude of works of about two-thirds of that in the three lines of Torres Vedras.
The works themselves, fewer in number, are generally much larger than those of Torres Vedras, and involve, I believe, when the amount of bomb-proof shelter is considered, more labor per yard of perimeter, but the latter lines involved a far greater amount of auxiliary work, such as the scraping of mountain slopes, palisading, abatis, roads, &c., than we have had occasion to make.
the lines of Torres Vedras armed with 534 pieces of ordnance (12, 9 or 6 pounders, with a few field howitzers); ours with 480 pieces, of which the greater number are 32-pounders on barbette carriages, the rest being 24-pounders on the same carriages, 24-pounder siege guns, 10, 20, and 30 pounder rifled guns (Parrott), with a few field pieces and howitzers.
As to number of guns, therefore, our armament approaches to equality with the famous lines mentioned. In weight of metal it more than doubles it.
The above applies to our works as now nearly completed, and has no reference to the additional works I have elsewhere mentioned as hereafter necessary. (Very considerable changes in works, armament, &c., have been made since the above account was written, which applies to their state when the Army of the Potomac left Washington, March, 1862.)
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It remains with me to express my sense of the zeal and efficiency with which the officers of engineers serving with me since last April have discharged their duties.
The theory of these defenses is that upon which the works of Torres Vedras were based, the only one admitted at the present day for defending extensive lines. It is occupy the commanding points within cannon range of each other by field forts, the fire of which shall sweep all approaches. These forts furnish the secure emplacements of artillery. They also afford cover to bodies of infantry. The works may be connected by lines of light parapets, or the ground (where practicable) may be so obstructed that the enemy's troops cannot penetrate the interval