Commanderie Saint-Jean, Medieval commandery in Strasbourg, France.

The Commanderie Saint-Jean is a group of medieval buildings at 1, rue Sainte-Marguerite, built from the first half of the 14th century to the first half of the 18th. From across the river, its main wing shows pale pinkish-brown stone, a steep roof of reddish-brown tiles with two rows of dormer windows and a squat chimney; a yellow building with dark-framed windows adjoins it. A brick wall with small rectangular windows and rounded openings carries pale plastered buildings with steep tiled roofs, a bell tower with a dark pointed spire and a clock with gold hands. It now houses the Strasbourg branch of the Institut national du service public.

The Knights of the Order of Saint John took possession of the complex in the 14th century and established a hospital there in 1520. The site later served as a prison from 1744 to 1988, before archaeological digs uncovered Gallo-Roman remains and medieval underground galleries.

The name Raspelhus, used for the prison that occupied the site, came from the prisoners' task of grating guaiac wood, a treatment for syphilis. Men were also set to gardening, rope-making, chair-caning, joinery, cardboard-making and printing; women sewed under the supervision of nuns. The small hospital building of 1520 still stands, its facade painted with trompe-l'oeil windows in the manner of Wendel Dietterlin.

The complex stands at 1, rue Sainte-Marguerite in the Gare district, and its buildings now house the Strasbourg branch of the Institut national du service public, so interiors are not open to casual visitors. A selection of artefacts from the 1989–1991 excavations is displayed in the reception hall. From the metal-railed bridge over the river, the stone wing with its steep tiled roof and dormer windows can be seen from outside.

The site concealed medieval underground galleries for centuries until archaeological excavations revealed them after the building ceased being a prison. These hidden passages demonstrate how the complex was expanded and adapted to serve different purposes over the centuries.