How was Roman citizenship, during the Roman Empire, proven?

by Shr3kk_Wpg

In the Roman Empire, Roman citizens enjoyed certain rights and priviledges. I was wondering how a Roman citizen would prove his (or her) citizenship, at least prior to the The Edict of Caracalla? Did they have papers they carried around with them?

Astrogator

Not to discourage other answers, but I answered a similar question in this thread.