Originally christened the Salon Elliptique (oval), it was subsequently called the Salon de la Rotonde because of the rounded shape of the large bay which projects into the garden and has three bay windows/doors opening onto it. It is located in the centre of the building.
The ceiling cornice of garlands of fruit and leaves, by the Huber Brothers, is identical to the one in the Salon du Congrès.
The imposts over the bays were decorated with acanthus leaves and heart shapes by the Derre Brothers.
Hippolyte Adams painted the pictures decorating the room.
The walls are covered by framed tapestries, The Gates of the Gods, woven in wool and silk at the Gobelins Factory between 1740 and 1774, after cartoons painted around 1699 by Claude III Audran. They depict: Venus or Spring, Ceres or Summer, Bacchus or Autumn and Saturn or Winter.
Neptune or Water and Jupiter or Fire were woven between 1722 and 1728.
Because of its form and aspect, this is one of the building’s pleasantest rooms. During the famous Congress of Paris, delegates used it for rest and relaxation and many important meetings have been held in it, including those of the international tribunal on the Baring Sea dispute at the end of 1893. Since 1989 it has been the Minister’s Office.
The main piece of furniture in this room is the desk known as the "Vergennes desk", which is in fact a reproduction. The original, made at the time of Louis XV and signed by Michon, is in the Louvre museum.
The "Vergennes inkstand/well", is in actual fact in Empire style and was ordered from the Odiot firm for Talleyrand on 3 December 1819. It was used for the signing of the Treaty of Paris in 1856. The drawing is by Fauconnier, head of the Odiot and Prudhon workshop. It depicts an Apollo Musagetes at whose feet two women hold a horn of plenty. Five muses are carved on the surrounding frieze: Polyhymnia (lyric poetry), Erato (music and pastoral poetry), Thalia (comedy), Melpomene (tragedy) and Clio (history). In the corners of the frieze are two lyres, surmounted by small tripods.