What is a Sally Port?

A sally port is a small, controlled space used in military constructions for defense. The entrance is usually protected by a sally port. Usually a fixed wall was built to block the door to make make it difficult for the enemy to fire directly inside from a distance. It is also explained in modern terms as an entrypoint into a secure facility. Openings to a sally port can only open one at a time. For example prisons use sally ports. When entering the prison areas, there are holding cells that have two doors. One door is unlocked at a time to allow a person to pass from one area into a secured area. After entering through the unlocked door, it is relocked and the other door is unlocked to allow them to enter. You can find more information here: