DUCK RIVER.

Across Duck River is a bridge 353 feet long resting on twelve trestles. It is protected by a double-cased block-house. For greater security to this important bridge another block-house was commenced last winter. From Tullahoma to Murfreesborough the road required protection from the numerous guerrillas that infested the country. Small garrisons at the stations and in the block-houses at the numerous river crossings guarded the road. The towns being small, no forts were built to control them.

MURFREESBOROUGH.

The city of Murfreesborough is situated about one mile and a half southeast of Stone's River. The country round about is generally level, and was formerly populous. One large fort near the city and depot, garrisoned by a regiment, would have controlled the place and neighborhood. A double-cased block-house would have been sufficient to protect the trestle bridge across Stone's River, 218 feet long. While General Rosecrans' army was encamped in the vicinity, Fortress Rosecrans, inclosing 200 acres on either side of Stone's River, was constructed under the direction of General St. Clair Morton, of the Corps of Engineers. This large work is composed of a series of bastion fronts, with small, irregular bastions and broken curtains; or more properly it may be described as consisting of lunettes connected by indented lines, having in the interior four rectangular redoubts, and one lunette as keeps to the position. In large permanent works, with high scarps, the ditches are swept by guns in the flanks, because the depression of the guns prevent the canister-balls from rising above the parapet. In field forts, with ditches only six feet deep and long curtains, opposite flanks cannot fire in the same manner as in permanent works without risk to the defenders; but by breaking the curtain line the ditches are swept by close musketry. This is the manner of flanking the ditches of Fortress Rosecrans. Its lines give powerful cross fires and direct fires, both of artillery and infantry, on all the approaches. Placed on the crests of the elevations, they not only command the distant country, but effectually sweep the gentle slopes within canister-range. This fortress could not be taken except by siege, if properly garrisoned and will defended. The parapets have high commands and when built were well revetted with fascines. The work has many traverses, covering against ricochet fire. Most of the guns are in embrasures, made with gabions. Lunetts Thomas and McCook and the four interior redoubts have large block-houses in the form of a cross. The magazines, except in Fort Brannan, are small. That in Lunette Mitchell is subject to being flooded, and is consequently useless in the wet season. The ditches of the redoubts are not so well preserved as those of the main lines. In fact the exterior slopes of the parapets and the scarps have taken the natural slopes, about 45 degress. These redoubts, however, are strong against attack, being defended by large keeps, which deliver their fire upon every part of the interior. It requires much labor to keep so large a work in repair; small portions of the parapets have sloughed off, due to frosts and heavy rains. These effects were especially noticeable in Lunettes Mitchell and McCook. Some thirty feet of the parapet revetment of Lunette Thomas had fallen down, when I inspected March 10. Parts of the revetted traverses in Lunette Negley were badly broken down, and I have been informed that the heavy and uncommon rains since have caused some further damage. Temporary