John Calvin's Commentary on the Bible - Acts 12:4
Verse 4 4.Adding four quaternions of soldiers. Luke doth, in this place, declare by circumstances that Peter was, as it were, shut up in his grave, so that it might seem that he was quite past hope; for as they divided the day and night into four parts by three hours, so Herod divided the watches, that four soldiers might always keep watch, and that one quaternion might succeed another every third hour. He showeth the cause why he was not forthwith put to death, because it had been an heinous... read more
Adam Clarke's Commentary on the Bible - Acts 12:7
Smote Peter on the side - He struck him in such a way as was just sufficient to awake him from his sleep. His chains fell off from his hands - The chains mentioned above, by which he was bound to the two soldiers. read more