The primary modern meaning for Sally port, derived from the French words for room "salle" and door "port", is a small controlled space with two doors. Essentially, one must enter the space and close the first door before opening the second to proceed.

Historical usage

A Sally port is a small, easily secured door in a castle wall or other fortification. During a siege, defending raiding parties would "sally forth" or "Sortie" from these ports and attack the besiegers. These raids would attempt to slow the offensive siege process. Targets for these raids included tools which could be captured and used by the defenders, labour-intensive works such as trenches and mines, and siege engines and siege towers. Sometimes enemy labourers were also targeted.

Modern usage

Modern personnel sally ports are used to control entry into highly protected and restricted military areas, i.e. nuclear weapons storage areas, highly sensitive (and large) conventional weapons storage areas, i.e. small arms, munitions, etc. Also, sally ports are used to control entry highly valuable civilian facilities such as currency or credit card manufacturing sites. A guard in a protected room will often control the middle space between gates checking credentials of anyone wants to pass through the second door. Sally ports are also used to restrict the flow of people to one at a time so that intruders cannot pass into the classified or secure area on a cleared person's coattails.

Military vehicular sally ports are similar to the personnel sally ports but have, of physical necessity, a large middle space to control the incoming/outgoing vehicle and personnel mounted in the vehicle. Mounted personnel are made to stand down and the vehicles are inspected by guard(s) a la (former) East German (DDR) Border Guards with mirrors on wheels and magnetic field detectors.

If the person or vehicle in the middle space is found to be unauthorized, the guard can "lock down" both gates trapping the individual in question until a guard or police response force can neutralize and remove the person and/or vehicle.

Word origin

Sally port may also be from the Latin 'salire' meaning to rush.

The common French word used to describe a Sally port is "poterne."

Source

• Continuing Education Program - Royal City of Eoforwic

Medieval defenses | Rooms