and report upon the plan of the present forts, and sufficiency of the present system of defenses for the city, " report as follows:

The system of works constituting what are called the Defenses of Washington may be divided into four groups; First, those south of the Potomac, commencing with Fort Lyon, below Alexandria, and terminating with Fort De Kalb, opposite Georgetown; second, those of the Chain Bridge; third, those north of the Potomac, between the Potomac and the Eastern Branch, commencing with Fort Alexander and terminating with Fort Lincoln; fourth, those south of Eastern Branch, commencing with Fort Mahan and terminating with Fort Greble, nearly opposite Alexandria.

The perimeter thus occupied, not counting the interval from Fort Greble to Fort Lyon, is about 33 miles or, including that, 37 miles.

In the first group are twenty-three field forts (including the small redoubts, Forts Bennett and Haggerty, and the external works of Forts Lyon and Blenker.) In the second group are two forts (Ethan Allen and Marcy) and three batteries for field guns. In the third are eighteen forts, four batteries permanently armed with heavy guns, besides about fourteen batteries for field guns, some of which are of heavy profile, with stockaded gorges, magazines, &c. In the fourth group are eleven forts (not including the outworks in progress of Fort Meigs), besides the armed battery connected with Fort Carroll. There are, therefore, in the whole system, as it now exists, fifty-three forts and twenty-two batteries.

In addition to these, is the small group consisting of Forts Ramsay and Buffalo and intrenchments on Munson's and Perkins' Hills, which do not properly belong to the fortifications of Washington.

The total armament in the different works at the date of this report, is six hundred and forty-three guns and seventy-five mortars. The total infantry garrisons required for their defense, computed at 2 men per yard of front perimeter, and 1 man per yard of rear perimeter of works, is about 25,000. The total number of artillerymen (to furnish three reliefs for each gun) required is about 9,000. Aggregate, 34,000.

It is seldom necessary to keep these infantry supports attached to the works.

The 25,000 infantry should be encamped in such positions as may be most convenient to enable them, in case of alarm, to garrison, the several works, and a force of 3,000 cavalry should be available for outpost duty, to give notice of the approach of any enemy.

The artillerymen, whose training requires much time, having learned the disposition of the armament and computed the distances of the ground over which attacks may be looked for, and the ranges and service of their guns, should not be changed. They should remain permanently in the forts. Whenever any enemy is within striking distance of the capital-able by a rapid march to attempt a coup de main, which might result in the temporary occupation of the city, the dispersion of the Government and the destruction of the archives all of which could be accomplished by a single day's possession- a covering army of not less than 25,000 men should be held in position to march to meet the attacking column. Against more serious attacks from the main body of the enemy, the capital must depend upon the concentration of its entire armies in Virginia or Maryland. They should precede or follow any movement of the enemy seriously threatening the capital.

The Commission do not deem it necessary to enter into a history of the construction of these works, though, fully to appreciate their merits or demerits, that history should be known (as it is presumed to be by