Hôtel de Cassini, Private mansion in 7th arrondissement, Paris, France

The Hôtel de Cassini is a private mansion with a U-shaped layout featuring a central building and two perpendicular wings. The interior displays marble flooring in the entrance hall, while the garden-facing side is defined by a mansard roof.

Claude Billard de Bélisard designed the hôtel in 1768 for Marquis Dominique-Joseph de Cassini, a military officer from the family of astronomers. In 1863 the comtesse de Talleyrand-Périgord had it rebuilt by Jean-Jacques Arveuf-Fransquin as a Louis XVI pastiche, adding a garden rotunda for boiseries from the hôtel de Monville. The State bought it in 1974.

During the early twentieth century, artists and writers gathered here when Cecil and Mimi Pecci-Blunt owned the property. The couple were patrons who attracted creative figures to their home.

The building has housed French government administrative offices since 1974, making it inaccessible to casual visitors. The exterior facade and courtyard remain viewable from the public street.

The rotunda beside the former library, called the Salle de la Chapelle, holds woodwork brought from the Hôtel de Monville, demolished for the cutting of boulevard Malesherbes. The panels are attributed to designs by Étienne-Louis Boullée. A matching room, the Salle des Marbres, keeps cherry-red marble panelling and Hungarian-point parquet laid by Arveuf-Fransquin.