What does Acts 27:1 mean?

After two years under house arrest in Caesarea Maritima for crimes he didn't commit, Paul appealed his case to Caesar (Acts 25:6–12). He's now on his way to Rome, along with Luke and Aristarchus (Acts 27:2). Aristarchus is apparently also a prisoner (Colossians 4:10); it's unclear if Luke is, but there's no reason to think so (Colossians 4:14). Later, Paul identifies Epaphras as his fellow prisoner, while Mark, Aristarchus, Demas, and Luke are depicted as free companions (Philemon 1:23–24). Luke doesn't explain where he has been during Paul's incarceration. It's reasonable to assume he spent time in Caesarea caring for Paul and in Jerusalem gathering information for his Gospel which tradition says was sent from Caesarea.

The Augustan Cohorts were honored units made of auxiliary troops. Guarding prisoners was probably not Julius' primary responsibility. Centurions were commanders of about one hundred troops and known for being steady, level-headed, and brave. Centurions in the New Testament have a good reputation. Jesus was impressed by the faith of a centurion who insisted Jesus could heal his servant from a distance (Matthew 8:5–13). The centurion at the cross watched Jesus die, and said, "Truly this was the Son of God!" (Matthew 27:54). The centurion Cornelius invited Peter to share the gospel with his house filled with Gentiles (Acts 10). Julius is kind to Paul and will—eventually—learn to trust him and even save his life (Acts 27:3, 30–32, 42–43).