Hôtel de Cassini

The Hôtel de Cassini is an 18th-century private mansion in Paris, standing at 32 rue de Babylone in the 7th arrondissement, just a short walk from the Hôtel Matignon, the official residence of the French Prime Minister.

Who built the Hôtel de Cassini, and when?

Construction began in 1768, commissioned by the Marquis Dominique-Joseph de Cassini, grandson of Jean-Dominique Cassini, the founder of the Paris Observatory. The architect Claude Billard de Bélisard, who had previously worked for the Prince de Condé, drew up the plans, while the building work itself was carried out by contractor Louis-Pierre Lemonnier. Several generations of the Cassini family were famous astronomers, so the townhouse on rue de Babylone served mainly as a mark of social standing rather than a working scientific residence.

How did ownership of the mansion change over time?

After the marquis's death, the property passed through several hands. In 1806 it was bought by General François Auguste de Caffarelli du Falga, an aide-de-camp of Napoleon I and governor of the Tuileries Palace. In 1825 it was sold on to Baron Jean de La Rochefoucauld. A later owner, the Countess of Talleyrand-Périgord, had the building largely rebuilt: architect Jean Jacques Nicolas Arveuf-Fransquin reworked the interiors into a pastiche of Louis XVI style and added a rotunda overlooking the garden, where fine period woodwork salvaged from the Hôtel de Monville was installed — panelling that still survives today.

Why is the building also called Hôtel Pecci-Blunt?

In the early 20th century the mansion was acquired by Cecil Blumenthal, known as Cecil Blunt, a wealthy American who wanted a Parisian residence to mark his marriage to Anna Laetitia — "Mimi" — Pecci, a great-grandniece of Pope Leo XIII. During the 1920s the couple carried out a thorough restoration of the house, while landscape architect Jacques Gréber redesigned the gardens. From that period onward the property has also carried the name Hôtel Pecci-Blunt.

What happens inside the mansion today?

The Pecci-Blunt family kept the house until 1948, after which it served for a time as lodgings for missionary priests passing through Paris. In 1974 the French government's Secretariat-General acquired the building for the Directorate-General for Administration and the Civil Service. Since then the Hôtel de Cassini has remained state property and now houses offices linked to the Prime Minister's services. It is not a museum and has no regular public opening hours — it functions as a working government building rather than a visitor attraction.

Are the facades and interiors legally protected?

Yes. The facades and roofs facing the street, courtyard and garden — excluding a 1963 extension at the back of the garden — were listed as a historic monument by decree on 17 June 1993. Two specific interior spaces received an even higher level of protection by decree on 10 July 1995: the oval salon overlooking the garden and the former dining room, known as the marble hall, on the ground floor. Protection therefore covers both the exterior structure and a small number of interiors judged to be of outstanding decorative value.

Frequently asked questions

Can visitors go inside the Hôtel de Cassini? No, not on a regular basis — the building is an active government office. Occasional access is sometimes possible during France's Journées du Patrimoine (European Heritage Days), so it is worth checking that year's official programme in advance.

Where exactly is the mansion located? It stands at 32 rue de Babylone, in the 7th arrondissement of Paris, close to the Hôtel Matignon and the gardens along the same street.

Why does it carry the name Pecci-Blunt as well as Cassini? The name comes from Cecil Blunt and his wife Mimi Pecci, who owned the mansion in the first half of the 20th century and financed its major 1920s restoration.

What are its most valuable architectural features? Art historians point to the oval garden salon and the marble hall as the finest surviving interiors, both singled out for protection by a separate 1995 decree.