The original circuit measured 17.261 km and was entirely unpaved when the 24 Hours of Le Mans first ran in 1923. The route ran south from the pits on the Rue de Laigné directly into the city of Le Mans, where drivers navigated a sharp hairpin near the Pontlieue bridge over the river Huisne before heading out along what would become the Avenue Georges Durand, named after the race's founding organizer. This configuration was as much a public road as a race track: surfaces were loose, sightlines were limited, and the relationship between the racing surface and everyday French life was entirely literal.
A first significant shortening came in 1929 when a bypass within the city reduced the circuit's overall length. The Pontlieue hairpin, a notorious bottleneck, was removed at that time, simplifying the run back toward the start and finish area and allowing faster average speeds.
The defining prewar layout emerged in 1932, when the city of Le Mans was bypassed altogether. A new section of track was added running from the pits via the Dunlop Bridge and through the Esses to the Tertre Rouge corner, which then fed cars onto the long straight toward Mulsanne. This produced the classic triangle configuration that would remain largely intact for decades: north along the pit straight, south on the long Hunaudières straight toward Mulsanne, then west and back north through Arnage.
In this form the circuit measured 13.492 km — compact by the standards of the original layout but still enormously long compared to any purpose-built road course of the time. The combination of the Mulsanne Straight, stretching nearly 6 km with no interruption, and the largely unmodified public road surfaces made the circuit simultaneously thrilling and treacherous.
Throughout the 1930s, the Circuit de la Sarthe rewarded cars capable of combining sustained high-speed endurance with mechanical reliability. The Mulsanne Straight — officially the Ligne Droite des Hunaudières, a section of Route Nationale N138 — allowed competitors to reach and sustain maximum velocity for extended periods, making it the fastest section of the course and the most punishing on drivetrains and tyres.
The pit straight itself was astonishingly narrow by modern standards, approximately 3.7 metres wide, shared without separation between moving race cars and the working pit crews. There were no barriers between the spectators and the racing surface in most sections. The Dunlop Bridge, added as part of the 1932 extension, became one of the circuit's defining landmarks and remained central to the layout for the rest of the circuit's history.
The prewar era of the Circuit de la Sarthe established the fundamental logic of Le Mans as a test of endurance rather than pure outright speed. Teams and manufacturers were forced to build cars that could sustain high-speed running across a full day and night cycle. Bentley dominated the race through the late 1920s, winning five times between 1924 and 1930. Alfa Romeo then took over in the early 1930s, followed by Bugatti and eventually the dominant French manufacturer Bugatti giving way to increasingly powerful machinery from Italy and Germany as the decade progressed.
The 1935 and 1937 editions saw competition from Bugatti, Delahaye, and Talbot-Lago, French manufacturers operating in a period when political and national identity were inseparable from motorsport. The race was suspended in 1936 due to a labor dispute in France, and the final prewar edition ran in 1939, after which the Second World War ended racing on the circuit until 1949.
The prewar circuit's layout — essentially the 1932 configuration — remained the backbone of the 24 Hours of Le Mans well into the postwar era. The Hunaudières straight would not be broken by chicanes until 1990, meaning that the fundamental character established before the war persisted for over fifty years. The circuit's identity as a test of machinery and crew over an unforgiving natural road environment, rather than a manicured permanent facility, is a direct inheritance from the prewar decades when the roads of the Sarthe were simply closed, marked, and raced upon.