In a series of Roman provinces a river forms the border of the Empire. In Europe this is the case for the provinces on the Rhine and the Danube. We know of three provincial fleets here, the classis Germanica, the classis Pannonica and the classis Moesica. Although one could conclude from their names that their areas of operations stretched over both provinces bearing their corresponding name, this was not the case. Thus, so-called military diplomas clearly show for the classis Pannonica and the classis Moesica that they belonged to the army of Pannonia Inferior and Moesia Inferior respectively
The Classis Moesica lasted until the beginning of the fifth century, being later assimilated within the Byzantine navy.