Navy and army

[Goffredo]

Was river patroling done by specialized troops (Navy or similar) or was it done by those stationed in forts along the limes? I would imagine that the Danube and the Rhine were partoled. Also a quick way to enter Germany (Drusus and then Germanicus) would be to enter along the rivers from the Channel (Ocean). I imagine there was a lot of naval and river activity during the Gothic problem in the third century (Black Sea and Danube). This type of activity was a Navy job but to go up a river is not the same thing as riding the ocean or sea waves. Did some degree of specialization occur over the centuries and "river marine corps" get created? <p></p><i></i>