without being exposed for considerable time to the destructive effects of the artillery or musk fire of the forts.

With such a system established, the defense against a powerful attack esquires that all the forts shall be garrisoned; that a certain amount of infantry, cavalry, and movable artillery be distributed along the lines sufficient to hold them until reserves can be brought to their support; and, finally, it requires a movable force held as reserve which may be shifted from point to point to meet the enemy's effort wherever it may be made, and where, aided by the works, they can repel superior numbers.

It is evident that without fortification a place cannot be considered secure unless held by considerably greater numbers than the enemy can bring to assail it. No less an authority than Napoleon says that, aided by fortifications, 50, 000 men and 3,000 artillerymen can defend a capital against 300,000 men, and he asserts the necessity of fortifying all national capitals.

The engineer forces attached to the Army of the Potomac as it was constituted during its campaign on the Peninsula consisted of a B brigade of two regiments of volunteer engineers (the Fifteenth New York, Colonel John McLeod Murphy, and the Fiftieth New York, Colonel Charles B. Stuart), commanded by Brigadier-General (Major of Engineers, U. S. Army) D. P. Woodbury, and of a battalion (three companies) of regular engineer troops, commanded by Captain J. C. Duane, Engineers.

The two regiments of volunteers had been placed under charge of Lieutenant-Colonel and Aide-de-Camp (Captain of Engineers, U. S. Army) B. S. Alexander in October, 1861, for instruction in the duties of engineer troops. The same officer had superintended, assisted by Captain Duane and Lieutenant Comstock, the getting up of pontoon trains and other engineer equipage. Previous to the embarkation of the army has was taken sick, and was thereby prevented from taking charge of the brigade, though he rejoined the army soon after its arrival before Yorktown.

The battalion of regular engineers was organized and instructed by Captain Duane, assisted by First Lieuts. C. B. Reese, C. E. Cross, and O. E. Babcock, which three last-named officers commanded the several companies of the same.

The engineer equipage consisted of about 160 bateaux, or wooden pontoons of the French model, with the necessary balks, chess, anchors, cordage, &c. There were also a certain number (of which I do not now find any exact statement) of Birago trestles and Russian canvas boats. As originally got up, this bridge equipage was organized in trains, of which there were six regular trains, consisting each of thirty-four French pontoons and eight Birago trestles, calculated to make a bridge of about 250 yards in length, and an advanced guard train composed of Birago trestles and Russian canvas boats. The wagons for but four of the regular trains and for the advanced guard train were provided.

All or nearly all the above bridge equipage was taken to the isthmus, but it did not retain its organization, except, I believe, one regular train taken along with the Engineer Battalion. The miscellaneous demand for bateaux for bridging Wormley's Creek at the siege of Yorktown, for quartermaster's use at Cheeseman's Landing, for the disembarkation of General Franklin's division, &c., rendered impossible and unnecessary the preservation of such an organization. A large portion of this equipage was in actual use for the purposes above named during the siege of Yorktown. On the advance of the army the single bridge train of the Engineer Battalion accompanied it, part of the remaining equipage