All the sources categories, epigraphy, literature and archaeology, together with the contributions of contemporary scientific methods form a solid foundation for the purpose of this paper: the study of the military hierarchy in Dacia. The most complex aspect is by far the hierarchy of soldiers. Epigraphic sources provide a rich source of data for Dacia but a less documented aspect is that of promotions and careers. Thus, the understanding of military hierarchy across the Empire is very valuable. Following the obvious hypothesis, that one cannot understand the history of Roman Dacia, unless in the wider context of the Roman Empire, the author attempts to decrypt the multitude of ranks and functions in the career of the solider. Thus, the research has moved from general to particular, starting from literary sources and contemporary monographic studies and reaching the individual epigraphic sources and studies concerned with a certain category of officers or a particular phenomenon found in an inscription. It was necessary to study each category of Roman units because the connections between them are very strong, especially as far as it involves soldiers, personnel and officers as elements of the whole functional entity in the Mediterranean space. For the purpose of systematization, the author chose the classification proposed by Domaszewski, more than 100 years ago, dividing the military ranks into several categories: soldier ranks - immunes and principales, centurions and primipili.