Quote Originally Posted by Uticensis View Post
I can't think of any example of such soldiers in the Republican or early Imperial Roman army. But in the sixth century Procopius describes Belisarius and Narses, whose armies were made up signifigantly of cavalry, dismounting cavalry when they needed infantry on the battlefield, and forming these dismounted horsemen into a "phalanx." Since a large number of soldiers in the army of the period were recruited from Germans, Slavs, and steppe people, this was tactic was probably adopted from the "barbarians."
In fact, there're many evidences of Roman cavalry fighting dismounted intentionally, and most of the time they won the day by this desperate resort, except in Cannae of course, but that time it was just a fatal misunderstanding.

Livy 3.62
The Sabines called strategy to their aid, for, after giving their line an extent equal to that of the enemy, they kept 2000 men in reserve to make an impression on the Roman left when the battle was at its height. By this flank attack they had almost surrounded and were beginning to overpower that wing, when the cavalry of the two legions-about 600 strong-sprang from their horses and rushed to the front to support their comrades who were now giving way. They checked the enemy's advance and at the same time roused the courage of the infantry by sharing their danger, and appealing to their sense of shame, by showing that whilst the cavalry could fight either mounted or on foot, the infantry, trained to fight on foot, were inferior even to dismounted cavalry.
Livy 4.38
Now in all directions they were giving way; in vain did Sempronius the consul remonstrate and encourage, neither his authority nor his dignity was of any avail. They would soon have been completely routed had not Tempanius, a decurio of cavalry, retrieved by his ready courage the desperate position of affairs. He shouted to the cavalry to leap down from their horses if they wished the commonwealth to be safe, and all the troops of cavalry followed his direction as though it were the order of the consul. "Unless," he continued, "this bucklered cohort check the enemies' attack, there is an end of our sovereignty. Follow my spear as your standard! Show Romans and Volscians alike that no cavalry are a match for you as cavalry, no infantry a match for you as infantry!" This stirring appeal was answered by shouts of approval, and he strode on, holding his spear erect. Wherever they went they forced their way; holding their bucklers in front, they made for that part of the field where they saw their comrades in the greatest difficulty; in every direction where their onset carried them, they restored the battle, and undoubtedly, if so small a body could have attacked the entire line at once, the enemy would have been routed.