2These positions, then, appertain to the senators. Passing now to the knights, the emperor himself selects knights to be sent out as military tribunes (both those who are prospective senators and the others; concerning their difference in rank I have already spoken), despatching some of them to take command of the garrisons of purely citizen-legions, and others of the foreign legions as well. In this matter he follows the custom then instituted by Caesar.