Roman citizens were free to travel throughout the Empire unimpeded, but how did they prove they were Roman? Did they have the equivalent of a passport?

by Cespur

Hello, on April Fools there was this topic with the exact same title as this one. However, there weren't given any serious answers (April fools harharhar). As it so happens to be however, I need to do some research into the history of immigration documentation/visas and I was wondering if anyone could answer the question for real this time! Thank you in advance.

_Keito_

This question has been asked a few times before. /u/ScipioAsina and /u/LegalAction gave a good answer here.