tions secured, as recommended by Colonel Alexander, the result of General Pope's campaign would probably have been different:

WASHINGTON, D. C., April 2, 1862.

SIR: You will proceed to Manassas at as early a moment as practicable, and mark on the ground the works for the defense of that place on the positions which I indicated to you yesterday. You will find two carpenters experienced in this kind of work ready to accompany you, by calling on Mr. Dougherty, the master carpenter of the Treasury Extension. The general idea of the defense of this position is to occupy the fringe of elevation which lies about half way between Manassas depot and the junction of the railroad with a series of works open to the rear, so that they may be commanded by the work hereafter to be described. There will be at least four of these works, three of them being on the left of the railroad leading from Alexandria, at the positions occupied by the enemy's works; the other on the right of this road, on the position we examined yesterday. The works of the enemy to the north of this latter position, numbered 1 and 2 on Lieutenant Comstock's sketch, may also form a part of the front line of our defense, but the sides of these works looking towards Manassas Station should be leveled, so that the interior of the works may be seen from the latter position. Embrasures should be arranged in all these works for field artillery. The approaches should be such that a battery can drive into the works. The number of embrasures in each battery will depend upon its size and the ground to be commanded. It is supposed there will be from four to eight embrasures in each battery.

The other works of the enemy looking towards the east and south may be strengthened, so as to afford sufficient defense in these directions. The work Numbers 3 in Lieutenant Comstock'c sketch may be also strengthened and arranged for field artillery when time will permit. This work is in a good position to cover a retreat, which would be made down the valley in which the railroad runs towards Bull Run. At Manassas Station there should be a fort constructed. The railroad will pass through this fort, and the depot, if there should be one built, should be placed in its rear. This latter work should be regarded as the key to the position. It should be as large as the nature of the ground will permit.

By going down the slopes, which are not steep, it may be made large enough to accommodate 2,000 or 3,000 men. The top of the position need not be cut away; it will be better to throw up the earth into a large traverse, which may also be a bomb-proof. Its profile should be strong and its ditches should be flanked. It should receive a heavy armament of 24 or 32 pounders, with some rifled (Parrott) 20 or 30 pounders. Its guns should command all the exterior works, so that these works could be of no use to the enemy should he take them. In accommodating the fort to the ground this consideration should not be lost sight of.

After tracing these works on the ground you will make a sketch embracing the whole of them, showing their relative positions and size. This sketch should embrace the junction of the railroads and the ground for some distance around the main work. It need not be made with extreme accuracy. The distances may be paced or measured with a tape-line. The bearings may be taken by compass.

Having located the works and prepared your sketch, you will report to Captain Frederick E. Prime, of the Corps of Engineers, who will furnish you the means of construction.

It is important that these works should be built with the least possible delay. You will therefore expedite matters as fast as possible.

Very respectfully, your obedient servant,

B. S. ALEXANDER,

Lieutenant-Colonel, Aide-de-Camp.

Captain FRED. R. MUNTHER, Present.

WASHINGTON, April 6, 1862.

SIR: I inclose you herewith a copy of the instructions which I gave to Captain Munther in reference to the defenses of Manassas.

As there has been a new department created (that of the Rappahannock), it is possible that you and I, as well as General McClellan, are relieved from the further consideration of this subject at the present time.

I will, however, state for your information, should the subject ever come before you again, that in my opinion the communication with Manassas by land should be secured..

To effect this in the best manner, so far as my observations extend, I think the bridge over Bull Run near Union Mills and just above the railroad bridge should be rebuilt or thoroughly repaired, and that a small work or two or three open batteries should be erected on the adjacent heights to protect it as well as the railroad bridge..

The communication by land would then be through or near Centreville, over the road used by the enemy.

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