Thirty very finished drawings and watercolours by Charles de La Fosse held in Würzburg form the puzzle of a mysterious ceiling decoration. Four sheets by Michel Corneille the Younger are the key: a copy from La Fosse in a private collection, two sections at the British Museum and the Courtauld Institute, and a complete project at the Musée des Arts Décoratifs. These suggest that in the second half of the 1680s the two artists successively responded to the same commission for a gallery and make the restitution of the structure and arrangement possible, as well as the identification of its scenes. Coming from the Hall of Mirrors, the decoration extols Louis XIV’s victories during the Dutch War, from the Passage du Rhin to the Traité de Nimègue. Oval compartments praise the virtues and campaigns of the prince, inspired by imperial coins. In Versailles as here, the history of the reign running through the grand décor seems to be enhanced by that of medals and its publication in 1702 by the Académie des Inscriptions et Belles-Lettres. The La Fosse and Corneille gallery mixes real and allegorical figures with mythological gods, without confusing the registers, as Le Brun does in the Hall of Mirrors. An old annotation indicates the intended site to be Château de Choisy, which is corroborated by plans and scales. Could it possibly be a commission from La Grande Mademoiselle after her break with Lauzun and the subsequent discontinuation of the gallery project on the theme of Venus?