An army drawn up for parade is usually disposed in two hues, with the infantry in the centre of each, and the cavalry on the wings; but this is far from being the case on service, since the nature of the ground will frequently reuder a contrary disposition necessary : in some parts of the field the troops may be in a single line, in other parts in two, or even in three lines.
The order of battle immediately previous to an engagement depends so much on the facility which the ground may afford for disposing and moving the troops, that it is scarcely possible to assign any rule fur the formation ; yet it is usual among military writers to class all the different dispositions of an army under two kinds, which are desig.
netted the parallel and the oblique order. The first comprehends all dispositions in which the troops of both armies may be engaged at once along the whole of their fronts : it was very generally employed by the Greeks and Romans, and during the middle ages : but it is now seldom adopted, since the weaker army is in danger of being out flanked; and should any part of it be driven back, the rest of the troops would either be turned and thus cut off, or be also compelled to retire. The battle would therefore be lost; and, being closely pursued, the defeated army incurs the risk of being entirely ruined, At the battle of Talavera, July, 1809, the two armies were drawn up in parallel order, and the attack was made by the French at the same time on the centre and on both wings of the allies.
The oblique order of battle may ho said to have been employed by the ancients when it was intended to break the enemy's line : on such occasions the phalanx was drawn up in the form of a wedge, and it advanced with an angle in front against the centre of the line. At the battle of Arbela, the army of Alexander attacked only the right wing of the Persians; and at the battle of Cynoseeplialw, the consul Flaini nius, ordering one of his wings to remain on the ground which it then occupied, advanced with the other against the army of Philip. (Polyb., ex. 3, lib. 17.) But this order of battle was first employed on sound military principles by Frederick III. of Prussia.
It does not always consist in drawing up an army in a straight line, which, if produced, would meet the line of the enemy; for this, on account of the inequalities and accidents of tho ground, is seldom possible: nor arc the two wings of an army always placed at unequal distances from those of the enemy, though this is frequently the case.
The principle of the oblique order consists in such a disposition of the troops as may enable a portion of the army to engage at some one point in the enemy s line, while the rest, protected by the obstacles of the ground, is stationed so as to be able to support the troops engaged, or prevent the enemy at other points of his line from attacking those troops in flank ; and a great commander will always manoeuvre so that his army, even though inferior on the whole to that of the enemy, may be superior in strength at the point of attack.
The attack is generally directed against one of the enemy's wings in the hope of being able to turn it, that is, to get beyond its extremity, or in its rear, and thus to cut off its retreat or intercept its supplies; but if tho wings are well protected by the ground, or by intrench inents, or by strong reserves being posted there, and if at the ammo time the centre has been weakened by troops having been drawn away, or by those which form it being widely disseminated, the attack may be advantageously made against that part of the line. At the battle of Corunna, January, 1308, the British and French armies were in oblique order, the right of the former being near the left of the latter ; while the opposite extremities were, by the nature of the ground, kept at a considerable distance from each other. The French made a charge with two strong columns, one of which advanced towards the British centre, and the other attempted to turn its right : in order to take this last column in flank, a part of the British army was placed obliquely to the line ; and its fire, together with that of the reserve, which was moved up to the support of the right wing, prevented the success of the manoeuvre. At the battle of Eekmillil (1809), Napoleon with his right wing attacked and defeated the left of the Austrians : by this success he cut them off from Vienna, and compelled them to retire towards Bohemia. Again, at the battle of Borodino, in 1812, the French attacked the Russian army at its centre and on its right wing, and succeeded in gaining the heights in that part of the position, after having suffered immense loss in storming a redoubt which protected them, and which was gallantly defended by the Elite of the Russian nfantry.