At that time, there were about three ways to obtain Roman citizenship:
1. Parents were born in the territory directly under Rome and have citizenship, and their children are Roman citizens. Maybe Paul's parents got Roman citizenship in Tarsus, so Paul said, "I was born a Roman." However, on other occasions, he emphasized that he was a Jew (12: 3) and said, "I am a Hebrew born of Hebrews" (Phil. 3: 4). That is to say, he and his father are Hebrews, Jews, but also Roman citizens.
Second, people who are not directly affiliated with the Roman Empire can apply for Roman citizenship if they serve the country and make meritorious service to the country.
Third, there are different ways to buy with money, just as many people get a country's passport in this way today. The commander-in-chief at that time also obtained Roman citizenship in this way. According to his full name Claudius Lucia (Acts 23: 33), it is proved that he was naturalized when Claudius became Caesar (Acts 1 1: 28).
God wants to use Paul vigorously, and he has already made all the plans, even this matter is in God's plan, which makes Paul get a lot of convenience in his missionary work.
It is said that Paul was beheaded when he died for the Lord and Peter was hung upside down on the cross. According to the laws of the Roman Empire, Roman citizens were not punished by crucifixion, because it was for slaves and prisoners belonging to the Empire.