Centurion

[Nathan Ross]

Did some centurions spend there entire career with a one legion? ... What would be the reason for a centurion to be transferred to so many legions?

Some centurions did stay with the same legion, paricularly in the earlier imperial period, Augustan to Julio-Claudian, when it appears that promotions were more in the hands of provincial governors, who could only promote within the legions in their province (or adjacent ones, it seems).

Later there was far more movement, and most centurions seem to have moved between at least two or three legions. Some moved far more often - Petronius Fortunatus moved thirteen times, back and forth across the empire. We don't really know why this happened - doubtless patronage played a part. But it does seem likely that the regular movement up the steps of the centurionate within each legion that Vegetius describes didn't happen in practice: a centurion who wanted or had earned promotion had to go wherever such a place was available. Sometimes they seem to have 'jumped' several steps in the hierarchy with a promotion; other times transferred men seem to have occupied the same position in a new legion, but perhaps one with better prospects for advancement.

The best study on centurion careers is J.R. Summerly's thesis Studies in the Legionary Centurionate (Durham University 1992), which has a mass of detail on all known centurions and their promotions and transfers over the centuries.

If you can find a copy of Ancient Warfare magazine, Special issue 2010, then D.B. Campbell's 'Backbone of the Legions: some centurions and their careers' also has lots of great detail on the topic.