Roman citizenship was until the latter stages of the empire not easily obtained or granted. However if people from conquered lands wanted to travel or settle throughout the empire they could. But make no mistake. Unless they were productive, they starved and withered. There was no welfare or charity to them. Economic realities defined borders. Today nobody who crosses into the EU or the US starves or freezes to death.
Allendale, the inhabitants of the cities got free food. That’s where the term “bread and circuses” to keep the voters happy, originated from