The Ottomans conquered Egypt in 1517. Cairo became the capital of the province of Egypt and lost much of its significance (even though it remained the second-most-populous city in the empire). The most interesting Ottoman monuments survive in the citadel. However, the Abdeen Palace is an exception. Construction began in 1863 on a piece of land owned by Abdeen Bey. The French architect Léon Rousseau designed a sumptuous royal residence that stuns visitors with its lavishness. An army of Egyptian, Italian, and French decorators and workers took ten years to complete and adorn the 500 rooms following the wishes of Isma'il Pasha, the Khedive (viceroy) of Egypt from 1863 to 1879. The palace served as Egypt's official government headquarters instead of the Citadel of Cairo, which had fulfilled this role since the Middle Ages.