In the late Roman empire, post-Diocletian, the Roman army looked very different than it did under the earlier Principate, and bore hardly any resemblance at all to the Republican legions that had turned the Mediterranean into a Roman lake.
The military was divided into two types of soldiers, one that stayed close to the Emperor and shuttled constantly from trouble-spot to trouble-spot, and another force that was strung all along the frontiers, divided between countless fortlets and watchtowers. These frontier troops spent their time working on fortifications and road maintenance when they weren't engaged in raiding the barbarians across the river or trying to drive off raids from those same tribesmen.
The frontier troops, known as limitanei, never saw much of the empire they were protecting. Since volunteering to spend your life filling potholes and fighting Franks in the chilly swamps of Germania Inferior wasn't the kind of thing that looks good on recruiting brochures, Diocletian simply decreed that if dad was a soldier, you were a soldier: In effect, garrisoning some godforsaken post in the ass end of nowhere became an hereditary life sentence that often as not ended with a retirement as a maimed veteran, eking out a living on the garrison farm, never having seen the Byzantium or Ravenna you'd spent your life protecting.
What got me thinking of this? This: