Ouvrage Four à Chaux was a grand ouvrage of the Maginot Line, located in the community of Lembach, France, in the Bas-Rhin département. Four à Chaux was adjoined by petit ouvrage Lembach and gros ouvrage Hochwald, and faced the German frontier. A "four à chaux" is a lime kiln in French, and the ouvrage was located in the area of a limestone quarry and kiln, which operated until 1939.
The ouvrage comprised eight blocks, with six combat blocks and two entries. The significant change in level between the combat blocks and the ammunition entrance required an inclined gallery immediately after the ammunition entrance. There was a 24 meter elevation difference between the ammunition entrance and the higher personnel entrance.
Four à Chaux is a position of medium importance on the Line, covering an area of 26 hectares, with a garrison of 477 men, 78 non-commissioned officers and 25 officers, 4.5 km of subterranean galleries and six combat blocks.
Block 1 was destroyed using explosives by the Germans before the surrender in 1945.
On 19 June, 1940, Four à Chaux and Lembach were bombed by German Stukas, with little effect .
Today, Four à Chaux is open to the public under the guidance of the SILE association. The guided visit includes Block 2, the barracks, principal gallery, usine and the museum. The ouvrage may be visited throughout the year.