The Centurion and his horse questions.

[jkaler48]

Apparently it was not uncommon for regular Legionaries in Caesar's time to know how to ride:
"caes.gal.1.42": [1.42] Upon being apprized of Caesar's arrival, Ariovistus sends embassadors to him, [saying] that what he had before requested as to a conference, might now, as far as his permission went, take place, since he [Caesar] had approached nearer, and he considered that he might now do it without danger. Caesar did not reject the proposal and began to think that he was now returning to a rational state of mind as he spontaneously proffered that which he had previously refused to him when requesting it; and was in great hopes that, in consideration of his own and the Roman people's great favors toward him, the issue would be that he would desist from his obstinacy upon his demands being made known. The fifth day after that was appointed as the day of conference. Meanwhile, as ambassadors were being often sent to and fro between them, Ariovistus demanded that Caesar should not bring any foot-soldier with him to the conference, [saying] that "he was afraid of being ensnared by him through treachery; that both should come accompanied by cavalry; that he would not come on any other condition." Caesar, as he neither wished that the conference should, by an excuse thrown in the way, be set aside, nor durst trust his life to the cavalry of the Gauls, decided that it would be most expedient to take away from the Gallic cavalry all their horses, and thereon to mount the legionary soldiers of the tenth legion, in which he placed the greatest confidence, in order that he might have a body-guard as trustworthy as possible, should there be any need for action. And when this was done, one of the soldiers of the tenth legion said, not without a touch of humor, "that Caesar did more for them than he had promised; he had promised to have the tenth legion in place of his praetorian cohort; but he now converted them into horse."