The _fascine_ is a bundle of twigs closely bound up, from nine to twelve inches in diameter, and from ten to fifteen or twenty feet in length. The largest are sometimes called _saucissons_. In making a fascine, straight twigs about the thickness of a man's finger are laid side by side, and firmly compressed together by a strong rope or chain attached to the extremities of two levers. While held in this position the twigs are firmly bound together by withs or cords. Fascines are used in constructing trenches, batteries, &c., and for filling up wet ditches. The _sap-fagot_ is a strong fascine about ten inches in diameter and two feet in length, with a picket inserted through the middle. It is used in the double sap in connection with gabions. _Sand-bags_ are usually made of coarse canvass. When filled with earth they are some six or eight inches in diameter, and from eighteen inches to two feet in length. From their perishable nature, they are used only when other materials cannot be procured, and where it is important to place the troops speedily under cover from the enemy's fire. Bales of wool, cotton, hay, straw, &c., may be employed in sapping for the same purposes as the above materials, when they can be procured in sufficient quantity. Pork and flour barrels, which are usually in abundance in a camp, are frequently filled with sand and used for forming magazines, blindages, &c., in field-works. A trench constructed in ordinary soil beyond the range of the enemy's grape, is called a _simple sap_, or ordinary trench. The earth is thrown up on the side towards the place besieged, so as to form a kind of parapet to cover the men in the trench. The labor is here executed under the supervision of engineer soldiers, by working parties detached from the other arms. Fig. 50 represents a vertical section of a simple sap. When within range of the enemy's grape, the _flying sap_ is resorted to in order to place the workmen speedily under cover. In this operation, gabions are placed in juxtaposition on the side towards the besieged work, and filled with all possible speed by the workmen. Three rows of fascines are usually placed on the top of the gabions to increase the height. The most difficult part of the flying sap is executed by engineer troops, and the trench is completed by the ordinary working parties. Fig. 51 represents a section of this sap.