Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/448

 434 FOKTIFICATION Demi-bastioned forts. Lines of redans Lines of tenailles Lines a cremaillere , Lines of bastions Lines broken, or with intervals 43. 44. 45. 46. 47. 48. The first class are of the simplest kind of field-works, and serve as cover in front of avenues, bridges (see fig. 49), causeways, and the like ; being open at the gorge, they are only used when their extremities rest on rivers, or on ob stacles which prevent their being turned, or when within the full sweeping fire of works in their rear. To increase the strength of a &quot; Redan &quot; its faces are sometimes broken into FIG. -Redan. FIG. 37. Double Redan. a kind of flank, as in fig. 36. In the &quot; Double Redan,&quot; or &quot; queue d hironde,&quot; fig. 37, the re-entering faces defend A B from SO to &amp;lt;SO Fas/is Fid. 38. Tenailled Heads. each other. &quot; Tenailled Heads&quot; (fig. 38) are used in situ ations which require a greater extent of front. &quot;Bas- From 22 to 43 Yards FIG. 39. Bastioned Heads. tioned Heads&quot; (fig. 39) are also employed in similar cir cumstances. &quot;Redoubts&quot; (fig. 40) are closed works of square or polygonal figure. In square redoubts provision should be made for defending the ground before the angles, which, how ever, are sometimes rounded or cut en cre maillere, so that a di rect fire may be de livered from them. Half-closed Redoubts, that is, redoubts in which the gorges are closed by thin parapets or timber stockades, may more fitly be classed here. They are employed when it is intended that their inter, or shall be open to artillery fire, so that an enemy having captured may not be able cither to retain them or to convert them to his own uses. Forts are works the parapets of which defend the ditches, and this distinguishes them from redoubts, the parapets of which do not. &quot; Star-Forts&quot; (fig. 41) are designed to deliver a cross fire from the adjacent sides ; but according to Jomini, they FIG. 40. Redoubts. are the very worst description of fortification ; they cannot have flanks, and the re-enter ing angles take so much from the in terior space that it is impossible to place troops and artillery in them sufficient for their defence,&quot; an opin ion confirmed by the practice of Sir Richard Fletcher and Sir John Jones in the construc tion of the lines of Torres Vedras. where the trace of FIG 41 Star-Forts. the redoubts was varied to suit the conformation of the ground. In &quot; Bastioned Forts,&quot; fig. 42, the flanking defence afforded by the para- A c. B pets to the ditches is nearly perfect. As bastioned forts are only constructed in special cases of im portance, no labour or expense should be spared in their forma tion. The bastioned face may be applied to any polygon pro vided that its angles are not less than 90. When the angles are less than 90 the FIG. 42. Bastioned Forts. salients of the bastions are too acute. &quot; Demi-bastioned Forts&quot; (fig. 43) inclose a greater in terior space than Bastioned Forts, but a portion of their FIG. 43. Demi-bastioned Forts. ditches are only defended by an oblique fire from the parapets of their faces. The parapets of all these works should be of sufficient thickness to resist the fire of the heaviest guns that can be brought against them. In some cases it will be necessary that the parapets should be strong enough to resist the fire of light field-guns, whilst in others it will be sufficient if they serve as a cover to the men within them against musketry. This latter cover is that which, when time for more does not avail, is thrown up at the close of a march,