At Eylau, Napoleon made a perpendicular attack on one wing at the same time that he sought to pierce the enemy's centre.
(Figure 21.) The concave order may be used with advantage in certain cases, and in particular localities.

Hannibal employed it at the battle of Cannae, the English at Crecy and Agincourt, and the Austrians at Essling, in 1809.
(Figure 22.) The convex order is sometimes formed to cover a defile, to attack a concave line, or to oppose an attack before or after the passage of a river.

The Romans formed this order at the battle of Cosilinum; the French at Ramilies in 1706, at Fleurus in 1794, at Essling in 1809, and at the second and third days of Leipsic in 1813, and at Brienne in 1814.
(Figure 23.) The order by echelon on one wing may be frequently employed with advantage; but if the echelon be made on both wings, there is the same objection to its use as to the perpendicular order on both wings.

At Dresden, Napoleon attacked both wings at the same time; this is the only instance in his whole history of a similar attack, and this was owing to peculiar circumstances in the ground and in the position of his troops.
(Figure 24.) The echelon order on the centre alone may be employed with success against an army formed in a thin or too extended line of battle, for it would be pretty certain to penetrate and break the line.
The echelon order possesses in general very great advantages.

The several corps composing the army may manoeuvre separately, and consequently with greater ease.