Camps designed to cover and guard a country, are constructed when the army has not sufficient strength to advance, or when the season prevents, or some other cause interferes with the prosecution of hostilities, while at the same time it is necessary to occupy a portion of the hostile territory. We have had numerous examples of this kind of camps--indeed, our armies occupy them generally while lying inactive during the winter. The character of the ground must always determine the shape and features of such a camp, but unless peculiar modifying circumstances dictate otherwise, the general form is that of the arc of a circle. This, with extensions at the sides to cover the flanks, and a rear guard, is the best for protection. The extent of this kind of camp is governed by circumstances, but is much greater, generally, than would be supposed. The camp of an army of 100,000 men, designed to cover any considerable district of territory, in a country where hills and rivers assist in giving protection, might have a front (including flanking parties of cavalry) of from 30 to 50 miles, and a depth of from 10 to 20; besides a continuous chain of forces in the rear, guarding communications with the base of supplies, from 10 to 50 miles distant. Camps in line of battle are generally established when opposing armies, lying in proximity, must be on the alert for attacks. They cover but little more ground than is required for the manoeuvres of the force, and are so arranged that, in case of probable conflict, the troops can assume immediately the formations of battle. Such camps are arranged in two or three lines, adapted to the natural features of the country for defence. The approach of the enemy having been communicated from the outposts, the tents are rapidly struck, the baggage loaded and sent to the rear, and in an hour the army is free from all encumbrances, and ready to meet the advancing foe. Usually, when armies lie in contact, expecting battle, the troops bivouac--no tents being pitched except at the headquarters of superior commanders, and at other places sufficiently in the rear to be free from immediate danger. The troops may be obliged to remain thus for a day or two, no fires being permitted in the advanced lines, so that their positions may not be indicated.