The Centurion and his horse questions.

[jkaler48]

Again, what "orders" are required while on the march? You're going to point B from point A. These orders would have been given out prior to leaving camp.

Changes in orders might be required based on reports from scouts, changes of orders received from higher headquarters, unexpected enemy actions or contact etc. I can think of some pretty bad disasters in later period warfare that resulted when changes to orders were not possible or for some reason not received. I am not convinced that changes to orders
would necessarily require Centurions to either appear in person to receive those changes or to be mounted to order to do so. So I don't think that the orders argument can be offered as proof of mounted Centurions on the march absent other supporting evidence.