The Castillo de la Real Fuerza (Castle of the Royal Force) is a fortress on the western side of the harbour in Havana, Cuba, set back from the entrance, and bordering the Plaza de Armas. Originally built to defend against attack by pirates, it has suffered from a poor strategic position too far inside the bay. The fortress is considered to be the oldest stone fortress in the Americas, and is listed as part of the UNESCO World Heritage site of "Old Havana and its Fortifications".

The fortress was not completed until 1577, with slaves and French prisoners providing most of the labour. Built of limestone quarried from the Havana shoreline, the fortification incorporated thick sloping walls, a moat and drawbridge. The governor, Francisco Carreño, ordered the addition an upper storey as barracks and a munitions store, but on completion, the fortress proved to be too small for practical use.

It quickly became apparent that the new fortress was too distant from the mouth of the harbour to serve effectively as a defensive bulwark, so it was instead adopted by Juan de Tejeda as the residence of the Governor of Havana.  The façade of the fortress was demolished in 1851 to allow O’Reilly Street to go all the way to the docks, and prevent El Templete, completed in 1828, from being overshadowed by the fortress.

The fortress was home to the National Archive from 1899 and the National Library from 1938 up until 1957. After the Cuban Revolution in 1959, it housed the offices the National Commission of Monuments and the Centre of Preservation, Restoration and Museology. Used briefly as the Museum of Arms, the conditions within the fortress were not conducive to the preservation of the displays. In 1977, on the 400th anniversary of completion, the building was inaugurated as a museum and used to display exhibitions of Cuban contemporary and international art. In 1990, it became the National Museum of Cuban Ceramics, but as of 2007, no displays are housed in the fortress. Some restoration work was carried out on the fortress prior to the inclusion of the fortification in the UNESCO World Heritage citation for Old Havana.