Centurions have been rightly compared to being roughly analogous to modern day junior to mid level officers, but was their career progression the same? Provided a Roman citizen secured a commission as a centurion, could they feasibly one day become a legate/General? How likely would it be, did it ever happen, and what would the typical career of a centurion look like?
Thanks!
In the Early to High Empire (let's say to 212 CE), there are only a few examples of centurions moving past their highest "natural" rank, which was primus pilus (first-ranked centurion of the First Cohort of the legion). Centurions were promoted from below, either due to merit or because someone higher up was helping them along. It seems like the vast majority were centurions most of their careers, either reaching the first rank or spending their whole life trying to get there (or not trying, perhaps).
A great and famous example is M. Petronius Fortunatus, who was a centurion in the 2nd half of the 2nd century CE. He was from Africa, and spent almost 50 years in service(!) without ever (apparently) reaching the First Rank. He spent his first four years in the army doing lower-level but important jobs (like signifer and optio) before making Centurion rank. He also traveled all over the world, from Moesia to Syria to the Rhine to Upper Pannonia to Britain to Numidia (back) to Syria (back) to Germania (back) to Britain to Arabia to Cappadocia to (maybe) Italia and finally to Pannonia again. Phew. His monument is CIL VIII 217.
If a centurion did reach the ranks of the primipilares, he was automatically elevated to the rank of equestrian (if he wasn't already) and became eligible for a big retirement bonus. With this money, many went back to their home towns and became important members of the community, perhaps laying the foundation for their children or grandchildren to rise farther (Keppie 1983 has some examples, mostly from the Late Republic at Beneventum). Of those who did reach the First Cohort (already a very small percentage of the total), a few were promoted directly beyond the glass ceiling to become a tribunus militum or praefectus castrorum. The PC was technically third in command, after the commander and any present legati. A primus pilus could be selected to return to Rome to command, as tribune, a cohort of vigiles, praetorian guard, or an urban cohort. They would then go back to the legion and be primus pilus bis / praefectus castrorum. Rankov (in Sabin et al 2007 v.2) suggests that this rotation of experienced men through the capital reinforced their loyalty to the Imperial court, which makes sense.
The best resource for this topic is probably still B. Dobson (1970), "The centurionate and social mobility during the principate" in C. Nicolet (ed.) Recherches sur les structures sociales dans l'antiquite classique, p.99-116.
as an add on: What did Maximinus Thrax's career specifically look like in practice? How much did birth determine centurion->general/emperor
This is a very broad question that would require a very long answer spanning the different phases and reforms of the Roman Army from the Republic to the late Empire - the role of Centurions and other junior officers changed quite a bit in the thousand or so years the rank existed. Could you narrow your question down to perhaps the Imperial or late Republic period?
To give you a quick example, we do have examples of Centurions rising in the late Imperial period to become Senators or even usurpers. Verus was a Centurion who rose to the rank of Senator during the 3rd century, becoming commander of the Legio III Gallica. Verus declared himself emperor in the winter of 218/19, but was executed soon after by Emperor Elagabalus. [1]
[1] - Thompson, G.R. "Elagabalus, Priest-Emperor of Rome." Ph.D. dissertation, University of Kansas p. 92. Also Greek coins in the British Museum.