At its zenith during the 2nd century AD, the Roman Empire was a vast and diverse entity, encompassing territories across Europe, North Africa, and the Middle East; estimates suggest that its population ranged from approximately 59 to 76 million people, with some studies proposing numbers as high as 100 million. The city of Rome itself was a bustling metropolis, with population estimates ranging from 450,000 to over 3.5 million inhabitants, though figures between 1 and 2 million are most commonly cited by historians. 

This immense population was a mosaic of various ethnicities and cultures, a reflection of the empire’s extensive reach and its incorporation of numerous peoples; it goes without saying that managing such a diverse and populous realm necessitated solid systems of legal identification to ensure clear records of citizenship and maintain social order.