Secret passage

Secret passages, also commonly referred to as hidden passages or secret tunnels, are hidden routes used for stealthy travel, escape, or movement of people and goods. Such passageways are sometimes inside buildings leading to secret rooms. Others allow occupants to enter or exit buildings without being seen. Hidden passages and secret rooms have been built in castles and houses owned by heads of state, wealthy individuals and criminals. These passages have helped besieged rulers to escape from their attackers, including Pope Alexander VI in 1494, Pope Clement VII in 1527 and Marie Antoinette in 1789. Passages and tunnels have been used by criminals, armies (notably the Viet Cong in the Vietnam War) and political organizations to smuggle goods and people or conceal their activities.

Secret passages often have hidden or secret back doors that are camouflaged so that they appear to be part of the fire wall, or so that they appear to be an architectural feature such as a fireplace, a built-in sliding bookcase or another feature. Some entrances are more elaborately concealed and can be opened only by engaging a hidden mechanism or locking device. Other hidden doors are much simpler; a trapdoor hidden under a rug can easily conceal a secret passage.

Some buildings have secret areas built into the original plans, such as secret passages in medieval castles. Some medieval castles' secret passages were designed to enable the inhabitants to escape from an enemy siege. Other castles' secret passages led down to an underground water source, which provided access to water during a prolonged siege.

Traditional Arabic houses sometimes have a "Bab irr": a secret door used as an emergency exit built into the walls and hidden with a window sill or a bookcase. The name comes from one of the six gates cut through an ancient wall in Aden (in modern-day Yemen), which was opened only in the event of a state security emergency. In modern-day Spain, the Arab fortress of Benquerencia has a Bab al-Sirr known as the "Door of Treason."

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