With the invention df gunpowder--atld its application to military gradual revolution took place in the general forms and details of fortification. Naked walls alone did not offer either suitable conveniences for the new military machines, or sufficient protection against the projectiles thrown from them. This led to the introduction of earthen ram parts and parapets which were placed against the walls and arson to meet the exigencies of the moment. The art received something like a scientific basis about this time in Italy, from which the names and forms of most of the elements of fortification now in use are derived. 'It was at this epoch that the bastioned form of fortification first appeared.
Bastioned System.— The improvements made in siege-artillery toward the end of the 16th century caused Sully, the Prime Minister of France, Grand-master of Artillery and Su perintendent of Fortifications, to take measures to modify and strengthen the fortifications then existing in France. The noted military engi neers, Errard, of Bar-le-Duc, De Ville and Count de Pagan, were successively charged with these modifications and left their impress upon the works entrusted to them. They were followed by Vauban, and he by Cormontaigne. Although modifications have been made in the bastioned system since the time of Cormon taigne, its essential basis is that of his method. A knowledge of the bastioned system would nqt be complete without an acquaintance with his method and those of Vauban.
A bastioned enceinte consists of a series of bastions, which occupy the salient angles of the polygon within which the enceinte is en closed; the flanks of the bastions being usually connected by straight curtains. The sides of the polygon which connect the salient angles of the bastions are termed the exterior sides, in contradistinction to the sides of an interior polygon which, being parallel to the first and occupying the positions of the curtains, are termed the interior sides. The polygon may be regular or irregular. The bastioned enceinte, when its relief and plan are suitably arranged, possesses the advantage of having its ditches thoroughly swept from within the enceinte itself, thus securing the flanking arrangement of the scarp; of bunging a cross and flank fire to bear upon the approaches on the salients of the enceinte; and furnishing a strong direct the length of curtain and to diminish ' tenor space in the bastion, the an= length has been restricted to 50 yardi The face of the bastion is usually e on the curtain-angle. In this case th
fire of the flank can be brought to beta enceinte-ditch along the foot of die wall of the face. Circumstances nay re a different position: directing it on srez‘ on the curtain, or on some point on th _ With the advantages gained there will responding disadvantages. Their relative will decide it. The relative positions and cross fire upon the site in advance of the curtains and the faces of the bastions.
The position of the flank will vary between the limits, a perpendicular to the curtain, and a perpendicular to the opposite face let fall from the point where the curtain intersects the line of defense. A position intermediate to these has been generally adopted; in most cases, placing the flank so as to make an angle of about 100 degrees with the curtain. The length should be sufficient to allow it to be armed with at least two pieces of artillery; this will determine the least length of flank. It may be increased beyond this, to any extent demanded by the circumstances of the defense. From the effect had in so doing to increase flanks and lines of defense, aid: respective lengths affect the length faces. If the line of defense is equal r: the distance between the curtain-agit opposite shoulder-angle, the cornsr: length of face will be zero; if the con<=. the flanks have their least and the line fense its greatest length, the renting will be the longest that we can have Bastioned Fort.— The bastioned le been devised to remedy defective flank: positions. It may consist of a polygut r: number of sides, but for field-forts and pentagon are generally preferred- 1:• a work of this kind, a square or first laid out, and the sides bisected i)" pendiculars, HI• a distance, GH, of one-eighth of a side in a square (one-seventh in a pen tagon) is set off on the perpendiculars; from the angular points of the polygon, lines DA, CF are drawn through the points thus set off ; these lines give the direction of the lines of defense; from the salients of the polygon, dis tances equal to two-sevenths of a side are set off on the directions of the lines of defense, which give the faces; from the extremities of the faces the flanlcs are drawn perpendicular to, or making an angle of 100 degrees with, the manned and vigorously defended. Another consideration that must not be omitted is the number of men that can be collected for work ing„ whether there are tools enough and time enough to do it.