Analysis of the few Roman auxiliary cohort documents in the archaeological record supports the idea that centurions of auxiliary cohorts regularly served away from their cohort on a variety of duties.
When considering Luke’s reliability as a historian, one of the areas of contention has been the Cornelius episode in Acts 10. Some commentators declare it anachronistic and not historical, maintaining that a Roman cohort was not present in Caesarea at the time Cornelius and Peter met. Others have proposed various alternatives, including Cornelius being retired or a centurion of Herod Agrippa’s troops. Many authors who address the issue of the Cornelius episode’s historicity do so by asking whether or not a Roman auxiliary cohort would be in Caesarea at that time, although in his Acts commentary Craig Keener includes a suggestion, supported by a historian of the Roman army, that centurions could be detached for service with smaller bodies of soldiers.
Although very few Roman auxiliary cohort documents (such as strength reports listing numbers and locations of soldiers in the cohort) have survived, two are from geographically separated parts of the empire, Britain and Africa. Common elements in those reports or lists suggest standard practices in the Roman army. One of those common elements is the absence from the auxiliary camp or fort of centurions who were engaged in duties away from the auxiliary cohort. A detached centurion might command his own century, but alternatively might command a smaller body of soldiers on some duty, perhaps relatively far away from the cohort.
Thus primary sources provide circumstantial evidence that even if a Roman auxiliary cohort was not stationed in Caesarea, Cornelius could have been detached from his cohort for duty in Caesarea, perhaps with only a small number of soldiers. Therefore Cornelius could be a Roman auxiliary centurion on active duty in Caesarea, perhaps even during Herod Agrippa’s reign and even if a large body of Roman soldiers was not present, on some undisclosed errand or long term duty, just as Luke implies.