The train departed Modane station at 11:15 p.m. and began its downhill run. The driver kept the speed as low as possible -- 10 kilometers per hour on the first incline. But the Culoz-Modane railway drops sharply through the Maurienne valley, and with nearly a thousand men aboard and only the braking technology of the era, the train began to accelerate beyond the crew's control. What happened next unfolded in minutes. The coaches, Italian-built and including two fixed-axle cars added at Modane, derailed with catastrophic force. The wreckage caught fire. Between the station at La Praz and a metal bridge farther down the valley, the train tore itself apart, scattering bodies along the ballast and right-of-way. Some soldiers jumped from the careening coaches; 37 of their bodies were later found strewn along the tracks. Others never had the chance.

The military hospital at Saint-Jean-de-Maurienne and the Bozon-Verduraz pasta factory nearby were pressed into service as field hospitals and mortuaries. Rescue teams pulled more than 424 identifiable corpses from the wreckage. Another 135 bodies were too damaged to identify. When roll call was taken on the morning of December 13, only 183 men answered their names. Over the following two weeks, more than 100 additional soldiers died in regional hospitals or while being transported to them. The final toll varied by source -- the declassified military report listed 435 deaths, while other records placed the number as high as 675 to 800. Each of these figures represented a soldier who had endured the Western Front, survived the chaos of Caporetto, and was within hours of embracing his family.

The French military clamped down immediately. Because the disaster implicated officers -- the very men who had left the overloaded train at Modane to ride the express -- the press was ordered to say nothing. Le Figaro, one of France's leading newspapers, devoted exactly 21 lines to the accident, four days after it happened. No outcry followed. No public investigation. A court-martial was eventually convened, but it tried six employees of the PLM railway company rather than any military officials. All six were acquitted. The disaster remained effectively classified for 90 years, one of the most thoroughly suppressed catastrophes in French history. It took until the early 21st century for the full story to emerge from declassified archives.

In 1923, Defense Minister Andre Maginot -- the same man who would later lend his name to France's famous fortification line -- inaugurated a monument to the victims in the cemetery of Saint-Michel-de-Maurienne. In 1961, the remains were transferred to the national military cemetery at Lyon-La Doua. A second monument was unveiled in 1998 at La Saussaz, near the actual crash site. The derailment remains the deadliest rail catastrophe in French history and the second deadliest in world history by confirmed casualties, exceeded only by the 2004 Sri Lanka tsunami train wreck. What distinguishes Saint-Michel-de-Maurienne is that it was purely operational -- no earthquake, no flood, no external force. Just an overloaded train, a steep gradient, and the decisions of men who chose the express.