22 Up to this word they listened to him. Then they raised their voices and said, “Away with such a fellow from the earth! For he should not be allowed to live.” 23 And as they were shouting and throwing off their cloaks and flinging dust into the air, 24 the tribune ordered him to be brought into the barracks, saying that he should be examined by flogging, to find out why they were shouting against him like this. 25 But when they had stretched him out for the whips,  Paul said to the centurion who was standing by, “Is it lawful for you to flog a man who is a Roman citizen and uncondemned?” 26 When the centurion heard this, he went to the tribune and said to him, “What are you about to do? For this man is a Roman citizen.” 27 So the tribune came and said to him, “Tell me, are you a Roman citizen?” And he said, “Yes.” 28 The tribune answered, “I bought this citizenship for a large sum.” Paul said, “But I am a citizen by birth.” 29 So those who were about to examine him withdrew from him immediately, and the tribune also was afraid, for he realized that Paul was a Roman citizen and that he had bound him.
(Acts 22:22-29 (ESV)
It was one of the nice perks of Roman citizenship that you could not be tortured. Non Romans could be tortured for any reason without trial. It was a rather brutal society in that way. If you weren’t a citizen you didn’t have many rights at all really. Paul is not afraid to assert his rights in his defense.