The lenght of service, currently denoted in Roman sources by the locution prolixitas stipendiorum, is the most important factor determining progression in rank, benefits and honorable discharge for the Militia armata and civilis. Especially in the complex administrative structure of late Antiquity, the length of service does not always coincide with the old age of the civil servant, and therefore “prolixitas stipendiorum” suggests properly the concept of “seniority”. This paper aims to provide an overview of some sources that particularly refer to the prolixitas stipendiorum as the criterion influencing Military and Civil Servants’ career, benefits and “Retirement Pensions”. Sometimes these sources appear very suggestive, not only because of the terminology, but also because of the content, taking account of the fact that their historical context precedes by centuries the ideas of Rule of Law and Social Security.