Were Romans forced to join the army?

Ordinarily no, they were not forced to join the army. However in the declining years, or in times of crises, the provincials would sometimes be conscripted. If the Romans had an agreement with an allied kingdom for troop supply, then the allied king could conscript in his own territory in order to supply Rome.
Ordinarily no, they were not forced to join the army. However in the declining years, or in times of crises, the provincials would sometimes be conscripted. If the Romans had an agreement with an allied kingdom for troop supply, then the allied king could conscript in his own territory in order to supply Rome.