The Roman cavalry initially faced foot soldiers who either did not fight in dense order, or did not have the proper training to withstand a cavalry charge, such as the Lygians, the Samnites or the Gauls.
Against these foot soldiers the frontal advance of a mass of cavalry made sense. The Roman cavalry were not exactly shock cavalry, like Alexander's Companions , but not even a cavalry force typical of the ancient world, comparable to most of the Greek, Iberian, Carthaginian and Galatian forces as it maintained the impetuosity of the elite of the Greek king.
Italy, Spain
Livy mentions that in 173 BC in a Roman-Lygian conflict, the Roman infantry failed to break through the opposing infantry. Then the Roman leader, the high priest Papilius ordered his cavalry to attack. The Roman cavalry was divided into three divisions with one to charge in front and the other two to flank the enemy.
The exact circumstances under which the battle was fought are not known. However, evidently fearing the double super-horn, or having fallen into disarray from their previous conflict with the Roman infantry, the Lygians lost their cohesion and the Roman cavalry broke their ranks , opening a rift in it. Passing through the rift, the Roman horsemen found themselves in the rear of their opponents and a general massacre ensued.
In 207 BC before the battle of the river Metauros the cavalry of the 3rd Legion, i.e. no more than 300 horsemen, attacked the Carthaginian infantry before it could deploy in battle formation and inflicted heavy casualties on it.
In 195 BC in Spain the Roman cavalry attacked the enemy flank but the Iberians managed to organize and repulsed it. These two examples are indicative of how to use cavalry against opposing infantry that had not yet received battle formation. There is a single record of Roman infantry prevailing against opposing infantry deployed in battle formation with its flanks protected.
Battle of Clastidium
In 222 BC the noble Claudius Marcellus moved against the Gauls who were threatening the city of Clastidium (present-day Casteggio) in Lombardy, at the head of about 5,000 horse and as many foot soldiers. The Gauls perceived the approach of their adversaries, and leaving a small force to guard the besieged city, drew up in battle formation.
The Gallic infantry formed a dense mass that only a breakdown in morale could break. The Roman cavalry charged immediately but were defeated by the mass and forced to retreat. But the Gauls, by thickening their center, weakened their flanks.
Marcellus saw their error and took advantage of it by ordering their horsemen to strike the enemy at both ends and once they were in his rear to attack again. So it happened. The Gauls this time because of the threat to their flanks and rear fled and were slaughtered by the pursuing Roman horsemen.
The Roman attack on the two enemy sides shook the morale of the Gauls, rendering them unable to react, "abusing the battle", as Polybius characteristically mentions, despite the fact that they outnumbered the Romans by a ratio of 3:1, as Plutarch mentions.
Battle of Telamonos
This victory of the Roman cavalry was never repeated in the period of the Republic. Rarely did the Romans throw their cavalry into battle against an infantry opponent without infantry support. An example of this tactic is the battle of Telamonos in Tuscany.
This battle was particularly important as Rome involved almost all of its front-line military forces. In the Battle of Telamonos, two Roman armies with a total of 75,400 men clashed against a Gallic army of 70,000 men. The Romans outnumbered infantry – 70,000 to 50,000 – but fell short in cavalry – 5,400 to 20,000.
The battle began with an attack by the Roman infantry against their respective Galatians. However, the fanatical Gauls, beyond all expectations, withstood the attack. Then the Roman commander Atilius Regulus ordered his cavalry to occupy a strategically important low hill covering the right flank of the Gallic infantry. The Roman cavalry managed to defeat the Gallic horsemen, despite the fact that they held higher ground and therefore advantage.
Immediately after and despite the heroic death of Regulus, the Roman cavalry ambushed the Gauls forcing them to retreat between the southern slopes of the hill and the sea, while the second Roman army under Aemilius Pappus had moved to their south. Surrounded on three sides with the only way out being the sea, the Gauls perished. Over 40,000 were killed and 10,000 captured. It is worth noting that in this battle the Gauls also used chariots.
Zama
The battle of Zama in 202 BC is perhaps the most typical case of perfect cooperation of the Roman infantry and cavalry in the field of honor. The Romans had a total of 6,100 horsemen, of which 4,000 were Numidian allies. The Numidians lined up on the right flank of the Roman line and the Roman cavalry on the left. The Romans had 2,000 Carthaginian horsemen against them. On the other side, the Numidian allies of the Romans outnumbered their opponents' cavalry 2:1.
The battle began with Hannibal ordering his 80 war elephants to charge against the enemy center. The Roman commander Scipio the Africanus, however, ordered his cavalry to blow loudly with the horns he had provided so that the elephants would be terrified.
The ploy partially worked and the Carthaginian left was thrown into disarray by the friendly panicked elephants. The Numidian horsemen took advantage of the confusion and, rushing in, overthrew the already far fewer Carthaginian horsemen.
But also the Roman left flank, the Roman horsemen rushed at their opponents and put them to flight with the first advance, pursuing them all the way to the Carthaginian camp. However, they did not get carried away and immediately reorganized and attacked the rear of the Carthaginian infantry which found itself thus surrounded and as a result was destroyed. The Carthaginian army lost all its men – 20,000 dead and 20,000 wounded, compared to 2,500 Roman dead and 4,000 wounded.
Galates, Celtiberians
In another case, in 193 BC the army of the emperor Cornelius Merula was fighting with the Gaulish tribe of the Boians. As mentioned by Titus Livius, the Gauls repelled the initial attack of the Roman legions. Then His Highness decided to launch a combined attack. At the time when his top infantry engaged the Gauls in front, his cavalry fell on the side of the Gallic formation, having apparently neutralized the opposing cavalry.
The Gauls tried to turn their front to meet the threat but the swift counter-reaction of the Roman and Latin cavalry allies prevented them. As the Roman historian reports, the Latin horsemen penetrated between the lines of the Gallic infantry causing confusion and then panic. Under the combined action of infantry and cavalry the Gallic line collapsed and the Roman cavalry pursued the defeated fugitives killing a large number of them.
Livius gives another example, this time from a battle between Romans and Celtiberians in Spain around 180 BC. The Celtiberians were considered the most warlike tribe of Spain and were a difficult opponent for the Romans. In the said conflict the Celtiberians organized their rushing infantry in a wedge formation and attacked the Romans splitting the Roman legions.
The situation was critical for the Romans, but fortunately for them the noble Quintus Fulvius Flaccus who commanded them decided to throw his cavalry into the battle against the enemy's human wedge. The Roman horsemen dressed up leaving the bridles of their horses so that they could run uncontrollably, but more impetuously. In this way they carried out two stormy raids.
As Livy mentions in the end there was not a horseman's spear that was not broken. Under the blows of the Roman cavalry, the Celtiberians began to "break" their formation with their lines disintegrating. The regrouped Roman infantry immediately intervened and broke up the enemy formation. As soon as the Celtiberians fled it was again the cavalry's turn to intervene and pursue them.