Trajan column equestrian order

[marcii ulpi messala]

I have observed that in the Trajan column, they all those who order and give the orders belong to the equestrian order, also the cavalry does the guards and other most frivolous tasks, while the infantry is the one that loads with the painful works and control is not observed between them was it the officialdom and subofiacialidad in this period always belonging to the cavalry?