I am very interested in the history of rome unfortunately I could only find the ranks but not how it worked. Did they have a place like west point where they would train oyou to become a higher rank, did you achive it only by being from a rich and influential family, did you move up by being brave on the battlefield?? Sorry for my mistakes not a native speaker :)
It was possible to distinguish yourself as a legionary to reach high positions of authority. Maximinus Thrax is the first to come to mind, going from legionary to later commanding the Legio IV Italica and even still claiming the title of emperor.