(formerly known as Citadel Investment Group, LLC) an American multinational hedge fund and financial services company.

a public military college in Charleston, South Carolina.

the German offensive operation in July 1943 against Soviet forces in the Kursk salient, proposed by Generalfeldmarschall Erich von Manstein during the Second World War on the Eastern Front that initiated the Battle of Kursk.

Citadel Securities LLC is an American market making firm providing liquidity and trade execution to retail and institutional clients, headquartered in Miami.

The Citadel of Cairo or Citadel of Saladin is a medieval Islamic-era fortification in Cairo, Egypt, built by Salah ad-Din (Saladin) and further developed by subsequent Egyptian rulers.

The (or the Fort of Qaitbay; ) a 15th-century defensive fortress located on the Mediterranean sea coast, in Alexandria, Egypt.

a large medieval fortified palace in the centre of the old city of Aleppo, northern Syria.

an archeological site at the center of downtown Amman, the capital of Jordan.

an adventure module for the 3rd edition of the Dungeons & Dragons fantasy role-playing game.

The Erbil Citadel locally called Qalat, is a tell or occupied mound, and the historical city centre of Erbil in the Kurdistan Region of Iraq.

a fortress in Berlin, Germany, one of the best-preserved Renaissance military structures of Europe.