The Citadel of Lille is a pentagon

Pentagon

In geometry, a pentagon is any five-sided polygon. A pentagon may be simple or self-intersecting. The sum of the internal angles in a simple pentagon is 540°. A pentagram is an example of a self-intersecting pentagon.- Regular pentagons :In a regular pentagon, all sides are equal in length and...

-shaped citadel

Citadel

A citadel is a fortress for protecting a town, sometimes incorporating a castle. The term derives from the same Latin root as the word "city", civis, meaning citizen....

 of the city wall of Lille

Lille

Lille is a city in northern France . It is the principal city of the Lille Métropole, the fourth-largest metropolitan area in the country behind those of Paris, Lyon and Marseille. Lille is situated on the Deûle River, near France's border with Belgium...

, in France. It was built around 1668. It hosts the Corps de réaction rapide France

Corps de réaction rapide France

Created on 1 July 2005, Headquarters Rapid Reaction Corps-France is a French headquarters, NATO certified, able to command a national or multinational land component of between 5 000 to 60 000 personnel....

.

Dubbed "Queen of the citadels" (Reine des citadelles) by Vauban

Vauban

Sébastien Le Prestre, Seigneur de Vauban and later Marquis de Vauban , commonly referred to as Vauban, was a Marshal of France and the foremost military engineer of his age, famed for his skill in both designing fortifications and breaking through them...

, it is one of the most notable citadels designed by Vauban. The citadel was part of a double line of fortified towns of Gravelines

Gravelines

Gravelines is a commune in the Nord department in northern France.It lies at the mouth of the river Aa 15 miles southwest of Dunkirk. There is a market in the town square on Saturdays. The "Arsenal" approached from the town square is home to an extensive and carefully displayed art collection....

, Dunkirk and Maubeuge

Maubeuge

Maubeuge is a commune in the Nord department in northern France.It is situated on both banks of the Sambre , east of Valenciennes and about from the Belgian border.-History:...

-Rocroi

Rocroi

Rocroi is a commune in the Ardennes department in northern France.The center was a fortified city, the walls of which are in the shape of a stylised star. The Battle of Rocroi was fought here.-Population:-External links:*...

. It was famous pré carré ("square field"), conceived by Vauban comprising 28 fortified cities.

Starting from Lille, Vauban supervised the construction of the many citadels and channels of the North, which controlled the border between France and Belgium.