Paul was  a prisoner headed to Rome. Julius guarded him.

Acts 27:

7 When the time came, we set sail for Italy. Paul and several other prisoners were placed in the custody of a Roman officer^[a] named Julius, a captain of the Imperial Regiment.² Aristarchus, a Macedonian from Thessalonica, was also with us. We left on a ship whose home port was Adramyttium on the northwest coast of the province of Asia;^[b] it was scheduled to make several stops at ports along the coast of the province.

³ The next day when we docked at Sidon, Julius was very kind to Paul and let him go ashore to visit with friends so they could provide for his needs.⁴ Putting out to sea from there, we encountered strong headwinds t