In field fortification an enormous quantity of work was done during our last war. Washington, Richmond, Nashville, Petersburg, Norfolk, New Berne, Plymouth, Vicksburg, and many other cities were elaborately fortified by field works which involved the handling of vast quantities of earth, and, where the opposing lines were near together, ditches, abbatis, ground torpedoes, and wire entanglements were freely used. In some cases the same ground was fortified in succession by both armies, so that the total amount of work expended, in this way, would have built several hundred miles of railway. Around Richmond and Petersburg alone the development of field works was far greater than Wellington's celebrated lines at Torres Vedras. In all future wars, when large armies are opposed to each other, it is probable that field works will play even a more important part than in the past. The great advantage of such works, since the introduction of the deadly breech loading rifles and machine guns, was shown at Plevna, where the Russians were almost annihilated in attempting to capture the Turkish intrenchments. SIEGES. It is not proposed to go into historical or other details of this branch of the subject, but to give in a condensed form some account of siege operations. According to the text books, the first thing to be done, if possible, in case of a regular siege, is to "invest" the fortress. This is done by surrounding it as quickly as possible with a continuous line of troops, who speedily intrench themselves and mount guns bearing outward on all lines of approach to the fortress, to prevent the enemy from sending in supplies or re-enforcements. As this line must be at considerable distance from the fort, it is usually quite long, and so is its name, for it is called the line of "Circumvallation." Inside of this line is then established a similar line facing toward the fort, to prevent sorties by the garrison. This line is called the line of "Countervallation," and should be as close to the fort as the range of its guns and the nature of the ground will permit. From this line the troops rush forward at night and open the trenches, beginning with what is called the first parallel, which should be so laid out as to envelop those parts of the fort which are to be made the special objects of attack. From this first parallel a number of zigzag trenches are started toward the fort and at proper intervals other parallels, batteries, and magazines are built; this method of approach being continued until the besieged fort is reached, or until such batteries can be brought to bear upon it as to breech the walls and allow the attacking troops to make an assault.