In olden times, 'sally port' referred to the small and secure door or gate in the outer wall of a fortification. Soldiers would make a swift passage through the secret and safe sally port. They would 'sally forth' to attack and weaken the besiegers. This would help in slowing the offensive siege process. So, it was a part of military engineering as an important technique to turn the tide on the attackers. Today, sally ports in a fortification are only there to remind us of historical tales. But, these doors have become a security device, rather, a foolproof system to guarantee a controlled entry and exit to some prominent areas. Porta, in Latin, means door; postern is another word used for the same. It also means an underground tunnel or passage. Salīre is the Latin word for 'to jump', or sortie. Sally is a tactical maneuver used by the military. Merriam Webster defines a sally port as: i) a gate or passage in a fortified place for use by troops making a sortie. ii) a secure entryway (as at a prison) that consists of a series of doors or gates. Access to certain areas are restricted for security reasons. No commoner is allowed to enter the campus. Military areas that are safeguarding a large number of weapons or facilities that house nuclear weapons, or such isolated sensitive storage areas need thorough security. Similarly, correctional facilities like prisons in several states across the country have to be well-guarded to avoid any inmates from escaping, and for their safety too. Another example is of the country's crucial financial institutions, like the United States Treasury building, which is safe pertaining to the plentiful security measures undertaken. One such measure to ensure that the facility remains intact and free from any possible danger entering or harming the institution is the installation of sally port doors. Considering the requirement of the beneficiary, these doors can be custom-made for optimum use. There are quite a few variations, including bi-fold, four-fold, rolling, or sliding doors. Vehicular sally port systems provide a way to manage controlled entry and exit of vehicles and personnel at the same time. Besides professional or government facilities, these are also employed for private buildings. Police sally ports are quite different; they are enlarged garage areas to allow controlled entry and exit of prisoners to a police vehicle. There is an organized way of operation for all kinds sally port doors. Usually, a facility houses a system of two separate sally port doors at the entry point to the campus. There is some space between these two doors (middle space); military vehicular sally ports can be large enough to occupy many military trucks at a time. A security guard is employed at a location far from the actual doors. He controls the following: i) the space between the two doors, ii) the operation of these doors, and iii) the movement of personnel, and/or materials, vehicles through the sally port. Before the First Door Opens The guard has to verify for the authenticity of all the people, escorts, or materials that are to enter the middle space. During Actual Transit He sees to it that no more than the maximum number of persons can move in or out of the protected space, at once. Before the Second Door Opens A separate controller of the interior protected space clears and permits any transit of people and/or materials. Also, the first door is to be locked and secured. Before the Second Door Closes The guard inspects whether the transit through the middle space is complete, and that it is empty. Overcrowding at the middle space is the greatest danger posed in this movement. In case of emergencies, it has to be executed with immense caution. Only one door can be opened at a time, resulting into too many people or vehicles crowded in the middle space. So, even if spaces are built after considering the average entry and exit load for that particular facility, lack of middle space can be a problem at times. However, for sally ports, there are overrides established for manual intervention and correction. Multiple openings and safety zones for internal evacuation are also built for emergency situations.