The Lille citadel, dubbed the "Queen of Citadels" by Vauban, was built between 1667 and 1670 after Louis XIV conquered the city. It was one of the kingpins of Vauban's famous Pré-carré lines of defense, composed of 28 fortresses. Listed as an "Historic Monument", this military structure stands out by its size, the quality of its architecture and its state of preservation. The Porte Royale, the main entrance to the fortress, is crowned with an insciption to the glory of the Roi Soleil (Louis XIV). The secondary entrance, or Porte Dauphine, is the "emergency exit" to let in reinforcements or evacuate. The Citadel retains its military role to this day, hosting an NATO-related army corps.