In a fortification with bastions, the citadel is the strongest part of the system, sometimes well inside the outer walls and bastions, but often forming part of the outer wall for the sake of economy. It is positioned to be the last line of defence should the enemy breach the other components of the fortification system. A citadel is also a term of the third part of a medieval castle, with higher walls than the rest. It was to be the last line of defence before the keep itself.
The oldest known structures which have served as citadels were built by the Indus Valley Civilization, where the citadel represented a centralised authority. The main citadel in Indus Valley was almost 12 meters tall. The purpose of these structures, however, remains debated. Though the structures found in the ruins of Mohenjo-daro were walled, it is far from clear that these structures were defensive against enemy attacks. Rather, they may have been built to divert flood waters.
In ancient Greece, the Acropolis (literally: "peak of the city"), placed on a commanding eminence, was important in the life of the people, serving as a refuge and stronghold in peril and containing military and food supplies, the shrine of the god and a royal palace. The most well-known is the Acropolis of Athens, but nearly every Greek city-state had one - the Acrocorinth famed as a particularly strong fortress. In a much later period, when Greece was ruled by the Latin Empire, the same strongpoints were used by the new feudal rulers for much the same purposes.
In various countries, the citadels gained a specific name such as "Kremlin" in Russia or "Alcazaba" in the Iberian Peninsula. In European cities, the term "Citadel" and "City Castle" are often used interchangeably. The term "tower" is also used in some cases such as the Tower of London and Jerusalem's (misnamed) Tower of David.
At various periods, and particularly during the Middle Ages, the citadel - having its own fortifications, independent of the city walls - was the last defence of a besieged army, often held after the town had been conquered. A city where the citadel held out against an invading army was not considered conquered. For example, in the 1543 Siege of Nice the Ottoman forces led by Barbarossa conquered and pillaged the town itself and took many captives - but the city castle held out, due to which the townspeople were accounted the victors (and took considerable pride in it).
Similarly, rebels who took power in the city but with the citadel still held by the former rulers could by no means regard their tenure of power as secure. One such incident played an important part in the history of the Maccabean Revolt against the Seleucid Empire. The Hellenistic garrison of Jerusalem and local supporters of the Seleucids held out for many years in the Acra citadel, making Maccabean rule in the rest of Jerusalem precarious. When finally gaining possession of the place, the Maccabeans pointedly destroyed and razed the Acra, though they constructed another citadel for their own use in a different part of Jerusalem.
As late as the 19th Century, a similar situation developed at Antwerp, where a Dutch garrison under General David Hendrik Chassé held out in the city's citadel between 1830 and 1832, while the city itself had already become part of the independent Belgium.
In time of war the citadel in many cases afforded retreat to the people living in the areas around the town. However, Citadels were often used also to protect a garrison or political power from the inhabitants of the town where it was located, being designed to ensure loyalty from the town which they defended.
For example Barcelona had a great citadel built in 1714 to intimidate the Catalans against repeating their mid 17th and early 18th century rebellions against the Spanish central government. In the 19th century, as soon as the political climate had liberalised enough to permit it, the people of Barcelona had the citadel torn down, and replaced it with the city's main central park, the Parc de la Ciutadella. A similar example is the Citadella in Budapest, Hungary.
The attack on the Bastille in the French Revolution - though afterwards remembered mainly for the release of the handful of prisoners incarcerated there - was to considerable degree motivated by the structure being a Royal citadel in the midst of revolutionary Paris.
Similarly, after Garibaldi's overthrow of Bourbon rule in Palermo, during the 1860 Unification of Italy, Palermo's Castellamare Citadel - symbol of the hated and oppressive former rule - was ceremoniously demolished.
The Siege of the Alcázar in the Spanish Civil War, in which the Nationalists held out against a much larger Republican force for two months until relieved, shows that in some cases a citadel can be effective even in modern warfare; a similar case is the Battle of Huế, where an NVA division held the citadel of Huế for 26 days against roughly their own numbers of much better-equipped US and South Vietnamese troops.
The Citadelle of Quebec still survives as the largest citadel still in official military operation in North America after more than two hundred years of existence.
A safe room on a vessel is called a citadel.
- Bijela Tabija (English: White Bastion) is a citadel overlooking the historic core of Sarajevo - National monument of Bosnia and Herzegovina
- Citadel Počitelj overlooking the historic village Počitelj and with it constitute architectural whole - National monument of Bosnia and Herzegovina
- Gradačac Castle is a citadel, also a palace of Husein "Dragon Of Bosnia" Gradaščević who was renowned 19th century military Bosnian Captain, overlooking the historic core of Gradačac - National monument of Bosnia and Herzegovina
- Bab Ksiba Southern gateway to the Kasbah, Marrakesh, first Citadel to the Sultans of Morocco
- Alcazaba a term for Moorish citadels in Spain
- Casbah/Kasbah a synonym
- El Morro
- Arx (Roman)
- Citadel of Arbil
- Citadelle Laferrière built by King Henry I of Haiti
- Citadelle de Forcalquier
- Acra (fortress)
- Antwerp citadel in 1830-32
- Citadel of Salah Ed-Din
- Edinburgh Castle
- Dublin Castle
- Prague Castle
- Tower of London
- Tower of David (Jerusalem)
- Kars#Kars Citadel
- Uzhhorod Castle
- Samuil's Fortress, Ohrid
- Spandau Citadel
- Suomenlinna (Finland)
- Rocca (architecture)
- ^ Sidney Toy (1985). Castles: Their Construction and History. Courier Dover. ISBN 0486248984.
- ^ Thapar, B. K. (1975). "Kalibangan: A Harappan Metropolis Beyond the Indus Valley". Expedition 17 (2): 19–32.
Fortifications Since ancient times Since Middle Ages
Arrowslit · Barbican · Bartizan · Bastion · Bent entrance · Bergfried · Caltrop · Castle · Concentric castle · Cheval de frise · Citadel · Curtain wall · Drawbridge · Enceinte · Embrasure · Fortified tower · Gate tower · Gabion · Glacis · Guard tower · Gulyay-gorod · Hoarding · Keep · Kremlin (Detinets) · L-plan castle · Machicolation · Moat · Motte-and-bailey · Murder-hole · Peel tower · Portcullis · Reduit · Shield wall · Toll castle · Tower house · Turret · Wall tower · Ward (Bailey) · Watchtower · Yett
Since Early modern period Since 19th century Fortifications by topography
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