The Romans had made but little progress in this arm when they encountered the Thessalians, who fought in the army of Pyrrhus.  They then increased their cavalry, but it was not numerous till after their wars with the Carthaginians.  Scipio organized and disciplined the Roman cavalry like that of the Numidians.  This arm was supplied from the ranks of the richest citizens, and afterwards formed an order intermediary between the Senate and the people, under the name of knights.

At a later period, the cavalry of the Gauls was particularly good.  The Franks were without cavalry when they made their first irruption into Gaul.  Under the reign of Childeric I. we see for the first time the “cavaliers francs” figure as a part of the national forces.  At the battle of Tours the cavalry and infantry were in the proportion of one to five, and under Pepin and Charlemagne their numbers were nearly equal.  Under Charles the Bald armies were composed entirely of cavalry, and during the middle ages the knights disdained the foot service, and fought only on horseback.

After the introduction of artillery, cavalry was still employed, though to little advantage.  Gustavus Adolphus was the first to perceive the real importance of this arm in modern warfare, and he used it with great success.  But it was left for Seidlitz to perfect it under the direction of Frederick the Great.

Marshal Saxe very justly remarked, that cavalry is the “arme du moment,” for in almost every battle there are moments when a decisive charge of cavalry will gain the victory, but if not made at the instant it may be too late.  The efficiency of cavalry depends upon the moral impression which it makes on the enemy, and is greater in proportion to the size of the mass, and the rapidity of its motion.  This last quality enables a commander to avail himself immediately of a decisive moment, when the enemy exposes a weak point, or when disorder appears in his ranks.  But this requires a bold and active spirit, which shrinks not from responsibility, and is able to avail itself with quickness and decision of every opportunity.  If it be remembered that it is essential that this coup d’oeil, so rare and so difficult to acquire, be accompanied by a courage and vigor of execution which nothing can shake, we shall not be astonished that history furnishes so few good cavalry generals, and that this arm so seldom does such execution as it did under Frederick and Napoleon, with Seidlitz and Murat as commanders.

The soldier gains great velocity by the use of the horse in war; but in other respects he is the loser.  The great expense and care required of the cavalier to support his horse; the difficulty experienced in surmounting ordinary obstacles, and in using his fire-arms to advantage, are all prejudicial to success.

The unequal size of the horse, and the great diversity in his strength and breed, have rendered it necessary to divide this arm into light and heavy cavalry, and a mixed class called dragoons.  The heavy cavalry is commonly used in masses where force is mainly requisite; the lighter troops are used singly and in small detachments, where rapidity of movement is most desired.