The stronghold of each series of trenches is the main firing trench in which the bulk of the defenders live. These trenches are wide and deep, and are floored with wood or hurdles. Each trench is divided into sections by means of a wall or traverse, jutting to the rear, and leaving but a narrow passage round it. By means of these traverses each section of the trench becomes a separate trench, and the whole of it cannot be enfiladed. The front towards the enemy consists of a parapet of sand-bags with loopholes, from which the men fire. As a rule, each trench is supplied with one or more machine guns. In many places the trenches are so close, and so keen a watch is kept, that it is highly dangerous for a man to show his head above the parapet. The enemy is observed through an arrangement of mirrors called a periscope. Some of the main trenches are roofed to afford head cover, and in the walls or in pits a little to the rear are the "dug-outs"--that is, caves into which the men retire to sleep or to take shelter when the shelling becomes hot. Some distance in front of the parapet there is a strong wire entanglement. If the wire has not been previously destroyed by artillery fire, it must be cut before the enemy can get into the trench itself. You notice that the trenches are not a fixture. Both sides "sap" towards their opponents' line, and drive mines forward until they are close to, or even under, the opposite trenches. In these mines charges are fired, and if successful, part of the trenches is blown in, and an infantry attack follows. More than once the miners of one side have found themselves separated from the miners of the other side by a mere wall of soil. Then there is feverish haste to fire a charge before the other side can do so. All through the day "snipers" are busy on both sides. They occupy pits, or craters made by shells, or ensconce themselves in ruins, or hide amidst the branches of trees, and try to pick off all opponents who show themselves. At night patrols steal out to the "No Man's Land" between the lines, and sometimes fall in with an enemy patrol and rush it with the bayonet. What are called "listening patrols" creep as near as possible to the opposite trenches, and try to overhear conversation, and find out what is going on in the enemy's lines. Each side burns flares to light up the darkness and make visible all movements in "No Man's Land." [Illustration: Bomb-throwers at Work. _By permission of The Sphere._] In this war every device which science can suggest is in use. In trench fighting, however, we have gone back to the ways of our forefathers. Mortars are employed to throw bombs into the enemy's trenches, and hand grenades, such as those used by the earliest grenadiers, are flung by each side. A correspondent of the _Times_ thus describes the bomb-throwers:--