Matthew Poole and continuators on Acts 21:31

31 And as they went about to kill him, tidings came unto the chief captain of the band, that all Jerusalem was in an uprore.

The Commander in chief over all the Soldiers there; or one that had the command over a Thousand. At the three great Feasts there was usually a considerable number of Soldiers at Ierusalem, the confluence from all parts being then so great, and the Iews so impatient of any Yoke or Government, the Romans durst not trust such multitudes without some check upon them. Thus at the Passover, when they took and crucified our Saviour, these Soldiers were made use of, Iohn 18.12.