Hôtel de la Guerre, 18th-century private mansion in Versailles, France

The Hôtel de la Guerre is a 18th-century mansion in Versailles originally built to serve as a military administrative center. The building displays flat vaulted ceilings made of brick and plaster, showcasing construction methods typical of the Louis XV period.

Construction began in 1759 under architect Jean-Baptiste Berthier to centralize military services and archives previously scattered between Paris and Versailles. The project was part of the broader modernization of royal administration under Louis XV.

The name comes from the ministry it served; the building is now called Hôtel de la Guerre – caserne Carnot. Only the Salon de Diane keeps its original decor: stucco paintings on the vault show the 1756 reversal of alliances, and the walls hold Charles Cozette's portrait of Louis XV on horseback at the 1745 Flanders campaign plus six canvases by Pierre Lenfant, painted 1757–1771, on the War of the Austrian Succession.

The building stands at 3, rue de l'Indépendance-Américaine, at the corner with rue Saint-Julien, a short walk from the Palace of Versailles. It now houses the Central Directorate of the Defence Infrastructure Service of the French Army, so the interior is not open to visitors. The monumental entrance portal, classified in 1922, can be seen from the street.

On 26 June 1762 Louis XV visited with the Dauphin, and Berthier set fire to a pile of wood and straw in one room to prove the flat brick-and-plaster vaults would hold; the flames did not reach the neighbouring rooms. The same vaulting, first used in northern France at the stables of the Château de Bizy, was repeated next door in the Hôtel des Affaires étrangères et de la Marine, built from 1761 under Choiseul.