On the field of battle the cavalry of the line is considered as the arm of the shock, to break through any corps that may be in opposition; but it is unable of itself to resist a shock, and therefore should on no account wait to receive the charge of another body of mounted troops.  It was on this account that Frederick directed his cavalry officers, under the severest penalties, never to receive a charge, but always to meet the attacking force half way.  This is the only mode of preventing defeat.

A good infantry can always sustain itself against the charges of cavalry.  At the battle of Auerstedt, in 1806, Davoust ordered the divisions of Gudin to form squares to resist the Prussian cavalry, which, by means of a fog, had gained a most advantageous position.  Bluecher led his cavalry in repeated and impetuous charges, but all was in vain; the French infantry presented a front of iron.  At the combat of Krasnoi, in 1812, the cavalry of Grouchy, Nansonty, and Bordesoult, attacked and overthrew the dragoons of Clarkof, but the Russian infantry under Neveroffskoi sustained itself against the repeated charges of vastly superior numbers of these French horse.  At the battle of Molwitz, the grenadiers sustained the charges of the enemy’s cavalry, although the cavalry of the great Frederick had already been completely overthrown.

But when the infantry is engaged with the infantry of the enemy, the charges of cavalry are generally successful, and sometimes decide the fate of the battle, as was the case at Rosbach, Zornsdorf, Wurtsburg, Marengo, Eylau, Borodino, &c.

Cavalry may also be very efficacious against infantry in wet weather, when the rain or snow renders it impossible for the foot soldiers to use their fire-arms to advantage, as was the case with the corps of Augereau, at Eylau, and with the Austrian left, at the battle of Dresden.  Again, if the infantry be previously weakened, or thrown into disorder by the fire of batteries.  The charge of the Russian cavalry at Hohenfriedberg, in 1745, is a remarkable example of this kind.

Cavalry should always be immediately sustained in its efforts either by infantry or other bodies of horse; for as soon as the charge is made, the strength of this arm is for a time exhausted, and, if immediately attacked, defeat becomes inevitable.  The charge of the cavalry of Ney on Prince Hohenlohe at the battle of Jena, and of the French horse on Gossa at Leipsic, are fine examples of the successful charges of cavalry when properly sustained.  Kunnersdorf and Waterloo are examples of the disastrous consequences of leaving such charges without support.

The choice of the field of battle is sometimes such as to render cavalry almost useless.  Such was the case at the battle of Cassano, between the Duke of Vendome and the Prince Eugene.  The field was so cut up by the Adda and the canals of Rittorto and Pendina, that Prince Eugene could make no use of his horse.  If, when master of the bridge of Rittorto, he had been able to charge the French with a body of cavalry, there had been no doubt of his complete success.