PARALLELS, in the attack or siege of a place (SIEGE), are wide trenches affording the besieging troops a free covered communication between their batteries and approaches, and a protection for the guard of the trenches and the covering parties in the day time. What were in farmer times termed lines of contravallation are now termed parallels. There are usually three or four parallels made in the attack of a place, though of course the number will depend wholly on the strength of, and the artillery possessed by, the garrison ; the saliency of its main works, and of its outworks and detached works, should it possess any ; the vigour of the defence and the nature of the ground in the neighbourhood, whether providing good natural cover for bodies of covering troops or not. Though the siege of different places will vary much according to these points, methods of attack are laid down in works on fortification on certain assumptions, in order to give an idea of the general method, and from which to deduce a standard of strength of different systems. In these there are generally three
parallels ; the first at 600 yards from the place, another at about 300 yards, and a third at the foot of the glacis. The second parallel is con structed by ;lying sap, the third by regular sap, while the first, being supposed out of the range of musquetry, grapeshot, and canister, by ordinary trench-work. These distances and methods may be much modified in practice, especially by the introduction of arms of pre cision, but as an assumption either for instruction or for comparing different systems they are still retained. The method of tracing, ke., will be found under SIEGE.