Hôtel d'Assy, Private mansion in Marais district, Paris, France

Hôtel d'Assy is a private mansion at 58 bis rue des Francs-Bourgeois in the 3rd arrondissement, built in 1642 by architect Pierre Le Muet for Denis Marin de la Chataigneraie. The building stands between courtyard and garden, with a light beige stone facade marked by pale vertical bands; its left upper section rises one storey higher than the rest. The ground floor has tall glazed doors with grey louvred shutters, and above are three windows per storey, the first floor with small wrought-iron balconies and the second with shorter curved-top windows.

The plot was part of a domain of Charles V's adviser Bureau de la Rivière, divided around 1531 and bought by Jacques Amelot, president of the Parlement. Denis Marin de la Chataigneraie, intendant of finances, had the first mansion rebuilt in 1642 by architect Pierre Le Muet. Louis Guillaume de Chavaudon added the north wing facing the garden between 1731 and 1733. The state bought the building in 1845 for the archives of the kingdom.

The name comes from Jean-Claude Geoffroy d'Assy, the tax-office cashier who owned the mansion in 1787; it is also called hôtel Marin de la Chataigneraie. Inside, a rocaille salon has overdoor panels depicting exotic birds, and the forged-iron stair railing with large baluster motifs dates from the end of Louis XIII's reign.

The mansion is accessible only through guided tours or exhibitions organized by the Archives nationales and cannot be freely visited. Visitors should check in advance which rooms and exhibitions are available on their intended visit date.

Jean-Claude Geoffroy d'Assy, the mansion's owner in 1787, had an observatory built on its roof for his children's tutor, the astronomer Jean-Baptiste Joseph Delambre. Delambre used it to carry out calculations for defining the metre, and it was demolished in 1910.