Hospitaller commandery of Saint-Jean-d'Acre, Medieval fortification in Acre, Israel

The Hospitaller commandery of Saint-Jean-d'Acre is a medieval fortification in Acre, Israel. The structure centers on a large courtyard surrounded by arcades, with deep wells and shallow pools for water storage, while the north wing contains vaulted rooms enclosed by thick exterior walls.

Founded after the Hospitallers moved to Acre's 12th-century north wall, the commandery is first documented in 1149 through the construction of the Saint-Jean church. Saladin took Acre in 1187; after the Frankish reconquest of 1191, with Jerusalem lost, the commandery became the order's headquarters. A building campaign from the late 12th to the 13th century added new wings and floors, until the city fell in 1291.

Two corbels carved with the fleur-de-lys, emblem of the French kings, survive in the northeast and southeast corners of the refectory, the 44 × 22 m two-nave hall of the south wing. Louis VII took the fleur-de-lys as his device during the Second Crusade of 1147–1149, and the Acre example may be linked to his visit in 1148. The hall is often wrongly called the Crypt of the Knights of St John.

The complex is split into four separately accessible sections: the Grand Manoir museum below street level, the Old Serail cultural centre, the Museum of Underground Prisoners in the Ottoman upper fortress, and the Diwan Khan art museum in the forecourt. Streets around the citadel and Old Serail lie seven to eight metres above the medieval level, the highest ground in Acre's old town. The Grand Manoir sits mostly beneath today's street level, reached by stairs.

The south wing's great hall, about 44 by 22 metres, is often wrongly called the "Crypt of the Knights of St John"; it is the refectory, roofed by rib vaults some 10 metres high on three massive piers. Two corbels in its corners carry the fleur-de-lys, emblem of the French kings adopted by Louis VII during the Second Crusade, possibly linked to his visit to Acre in 1148.