Herod Agrippa I, having put James the brother of John to the sword, and seeing it pleased the Jews, arrested Peter also during the feast of Unleavened Bread. Peter was held in the Antonia Fortress, guarded by four squads of four soldiers, intended for public execution after Passover.
On the night before the trial, with sentinels at the door, Peter was sleeping between two soldiers, bound with two chains. An angel of the Lord appeared; light shone in the cell. The angel struck Peter on the side and woke him: 'Get up quickly.' The chains fell off his hands. 'Dress yourself and put on your sandals... wrap your mantle around you and follow me.' Peter went out and followed, thinking he was seeing a vision. They passed the first and second guards, came to the iron gate that opened into the city — and it opened to them of its own accord. They went out and passed on through one street; then the angel left him.
Peter came to himself and went to the house of Mary, the mother of John Mark, where many were gathered praying for him. A servant girl named Rhoda, recognising his voice at the door, ran inside in joy without opening — and was disbelieved by the assembled Christians ('You are mad'; 'It is his angel'). Peter kept knocking until they opened. The episode is the canonical image of the prayer of the Church for those imprisoned for the faith.