is nevertheless an important work, as, taken in connection with Forts Richardson, Craig, &c., it completes a defensive line for Washington independent of the extension of Alexandria..

The defense of Alexandria and its connection with that of Washington was a subject of anxious study. The exigency demanding immediate measures, the first idea was naturally to make use of Fort Ellsworth as one point of our line, and to connect it with Fort Scott by an intermediate work on Mount Ida. An extended study of the topography for several miles in advance showed that such a line would be almost indefensible. Not only would the works themselves by commanded by surrounding heights, but the troops which should support them would be restricted to a narrow space, in which they would be overlooked and harassed by the enemy's distant fire. The occupation of the eights a mile in advance of Fort Ellsworth, upon which the Episcopal Seminary is situated, seemed absolutely necessary. The topography proved admirably adapted to the formation of such a line, and Forts Worth and Ward were commenced about 1st of September, and the line continued simultaneously by Forts Blenker and Richardson to connect with Forts Albany and Craig. Somewhat later the work intermediate between Blenker and Richardson-filling up the gap and having an important bearing upon the approaches to Forts Ward and Blenker and the valley of Fourth Mile Run-was commenced..

The heights south of Hunting Creek, overlooking Alexandria and commanding Fort Ellsworth, had been always a subject of anxiety. The securing to our own possession the Seminary Hieghts, which commanded them, diminished materially the danger. As soon, however, as a sufficient force could be detached to occupy those heights and protect the construction of the work it was undertaken, and the large work (Fort Lyon) laid out and commenced about the milled of September..

Previous to the movement of the army defensive measures had been taken at the Chain Bridge, consisting of a barricade (bullet proof, and so arranged as to be thrown down at will) across the bridge, immediately over the first pier from the Virginia side, with a movable staircase to the flats below, by which the defenders could retreat, leaving the bridge open to the fire of a battery of two field guns immediately at its Maryland end, and a battery on the bluff above (Battery Martin Scott) of one 8-inch sea-coast howitzer and two 32-pounders. As even this last battery was commanded by heights on the Virginia side, it was deemed proper, after the return of the army, to erect another battery (Battery Vermont) at a higher point, which should command the Virginia Heights and at the same time sweep the approaches of the enemy along the Maryland shore of the Potomac..

During the months of May and June the country between the Potomac and the Anacostia had been examined mainly with the view of obtaining knowledge of the roads and defensive character of the ground, not in reference to locating field defenses. At the period now in question there was apprehension that the enemy might cross the Potomac and attack on this side. Of course what could be done to meet the emergency could only be done without that deliberate study by which a complete defensive line would best be established. The first directions given to our labors were to secure the roads, not merely as the beaten highways of travel from the country tot he city, but also as in general occupying the best ground for an enemy's approach..

Thus the sites of Forts Pennsylvania, Massachusetts, Slocum, Totten, Bunker Hill, Saratoga, and Lincoln were rapidly chosen, and works commenced simultaneously at the first, second, third, and sixth of these.