Wellington, at Waterloo, formed the parallel order with the retired crotchet on the right flank.
(Figure 16.) A line of battle parallel to the enemy's, if strongly reinforced on one point, is according to correct principles, and may in certain cases secure the victory; but it has many inconveniences.

The weak part of the line being too near the enemy, may, notwithstanding its efforts to the contrary, become engaged, and run the risk of a defeat, and thereby counterbalance the advantages gained by the strong point.
Moreover, the reinforced part of the line will not be able to profit by its success by taking the enemy's line in flank and rear, without endangering its connection with the rest of the line.
(Figure 17) represents the parallel order reinforced on the centre.

The same remarks are applicable to this as to the preceding.
These two orders were frequently used by the ancients: as at the battle of Zama, for example; and sometimes by modern generals.

Turenne employed one of them at Ensheim.
(Figure 18) is the simple oblique order.
(Figure 19) is the oblique order, with the attacking wing reinforced.
This last is better suited for an inferior army in attacking a superior, for it enables it to carry the mass of its force on a single point of the enemy's line, while the weak wing is not only out of reach of immediate attack, but also holds the remainder of the enemy's line in check by acting as a reserve ready to be concentrated on the favorable point as occasion may require.
The most distinguished examples under this order are the battles of Leuctra and Mantinea, under the celebrated Epaminondas; Leuthen, under Frederick; the Pyramids, Marengo, and Jena, under Napoleon.
(Figure 20.) An army may be perpendicular upon a flank at the beginning of a battle, as was the army of Frederick at Rosbach, and the Russian army at Kunersdorff; but this order must soon change to the oblique.

An attack upon both wings can only be made when the attacking force is vastly superior.