φύλαξ

Saying, The prison truly found we shut with all safety, and the keepers standing without before the doors: but when we had opened, we found no man within.

And when Herod would have brought him forth, the same night Peter was sleeping between two soldiers, bound with two chains: and the keepers before the door kept the prison.

And when Herod had sought for him, and found him not, he examined the keepers, and commanded that they should be put to death. And he went down from Judaea to Caesarea, and there abode.