C

“There was one obligation that the Romans imposed on all those who came under their control: namely, to provide troops for the Roman armies. In fact, for most of those who were defeated by Rome and forced, or welcomed, into some form of ‘alliance’, the only long-term obligation seems to have been the provision and upkeep of soldiers. These peoples were not taken over by Rome in any other way; they had no Roman occupying forces or Roman-imposed government. Why this form of control was chosen is impossible to know. But it is unlikely that any particularly sophisticated, strategic calculation was involved. It was an imposition that conveniently demonstrated Roman dominance while requiring few Roman administrative structures or spare manpower to manage. The troops that the allies contributed were raised, equipped and in part commanded by the locals. Taxation in any other form would have been much more labour-intensive for the Romans; direct control of those they had defeated would have been even more so.”
― Mary Beard, SPQR: A History of Ancient Rome