Acts 22:29
Then straightway they departed from him which should have examined him: and the chief captain also was afraid, after he knew that he was a Roman, and because he had bound him. Then straightway they departed from him which should have examined him: and the chief captain also was afraid, after he knew that he was a Roman, and because he had bound him.
When those preparing to examine Paul learned that he was a Roman citizen, they immediately stopped and withdrew at once, releasing him from the threatened examination. The chief captain also was afraid after he knew that Paul was a Roman, and because he had bound him, having himself ordered Paul bound. That binding violated the protections that Roman citizenship gave.
Paul stated that he was free-born, unlike those who had obtained citizenship by paying for it, buying their freedom. Roman citizenship carried privileges that protected him from unlawful treatment, including binding and examination and degrading violence by unbelievers. This fits the pattern in which heathen magistrates delivered Paul when Jewish authorities sought to harm him, while Jewish tribunals condemned him without proving his guilt.