Based on Acts 12:1-19

And when Peter was come to himself, he said, Now I know of a surety, that the Lord hath sent his angel, and hath delivered me out of the hand of Herod. Acts 12:11.

The day of Peter's execution was at last appointed, but still the prayers of the believers ascended to heaven; and while all their energies and sympathies were called out in fervent appeals for help, angels of God were watching over the imprisoned apostle.... CC 336.2

Herod on this occasion had taken double precautions. To prevent all possibility of release, Peter had been put under the charge of sixteen soldiers, who, in different watches, guarded him day and night. In his cell, he was placed between two soldiers, and was bound by two chains, each chain being fastened to the wrist of one of the soldiers. He was unable to move without their know ...