saillie

Sally port combines sally (from the Old French saillie, from the Latin salīre: to leap, to spring) with port (from the Latin porta: gate). A sally is a sudden offensive rush from a defensive position. A sally port is the gate through which that rush happens. The word captures the violence of the action — defenders leaping out of their fortress to attack the besiegers — in a single syllable derived from jumping.

Sally ports were typically small, inconspicuous doors set into fortress walls, often at ground level in places difficult for besiegers to observe or block. They were designed for speed and surprise. A garrison locked inside a fortress was passive — slowly starving, slowly losing morale. A sally through a hidden door transformed defenders into attackers, even if only for an hour.

The most famous sallies in military history changed the outcomes of sieges. During the Siege of Malta in 1565, Knights Hospitaller made repeated sallies against Ottoman forces from Fort St. Elmo and the Borgo. At the Siege of Sevastopol in 1854-55, Russian sallies disrupted Allied siege works repeatedly. The sally port was the mechanism that made these counterattacks possible — without it, a besieged garrison had no offensive capability.

Modern military installations still have sally ports, though the term now refers to any controlled-access entry point with two doors that cannot be open simultaneously. Prison sally ports work the same way — a vestibule with interlocking doors. The leaping offensive rush has been replaced by controlled entry, but the name persists. The port that allowed leaping now prevents it.