The Voie Sacrée (the Sacred Way) is the reason of the French victory during the Battle of Verdun in 1916 as, while the majority of the roads at that times were of dust and the great axis and that the railway between Bar-le-Duc and Verdun was cut but the enemy bombings, the Voie Sacrée, a large rock road long of 75km between Bar-le-Duc and Verdun was used to carry all the material and the men by lorries to the city of Verdun.

It's thanks to the General Pétain that the supply line to Verdun was created and maintained as he requested to the Régiments du Train (Litteraly "train regiments", it's the supplies corps of the French Army created under Napoléon) to stay on the edges of the Sacred Way 24/24h, 7/7d, in order to maintain the road in a good enough state to allow the thousands of lorries to circulate between Bar-le-Duc and Verdun. One can counts that the average rate of circulation on the Voie Sacrée is of a lorry every 14 seconds and the both sides were used, the line Bar-le-Duc - Verdun to bring the men and the supplies to the first line and the line Verdun - Bar-le-Duc was used to transport wounded soldiers and soldiers on leave behind the lines. At every hours of the day as at every hour of the night during the whole Battle of Verdun, the men of the Train were working to keep the traffic as fluid as possible, throwing rocks under the trucks to maintain the road and pushing the broken lorries on the roadside in order to fix them later. The road was a kind of giant carousel as the lorries were continusly doing the ride between the arrival railway station to a little village at 8km from Verdun from were the soldiers had to walk to get to the fortress and as both the departure and the arrival were in a kind of roundabout.
Though it's now called the Sacred Way, the name that soldiers called it during the war was simply "La Route" (The Road) and it's only after the war that the writer Maurice Barrès gave it the nowadays name which stuck in the time.

From the beginning to its end, the Voie Sacrée is marked out at every kilometre by one of those markers which isn't much different of the distance markers of the inter-war/post-war era but which differs by, by other means than the writing on them, the presence of a bronze Adrian Modèle 1915 helmet ornamented by a crown of laurels. After a reform in 2006 where the "national roads", called RN, were classed as "departemental roads", called D or RD, the road passed from the official name of RN35 to RD1916, to pay a tribut of the Battle of Verdun but in 2007, a decree was passed to give it the name of Voie Sacrée Nationale, name that it kept and that can be seen on maps.
The Voie Sacrée is also the only place in France to have a monmuent to the men of the Train, it's an obelsik of a dozen of metres high and which has in its upper part the insignia of the Train Regiments, a winged wheel, and a bit behind, there's a frieze with engravings of the action of the men of the Train during the war.

(I'm really sorry for the high-tension line in the background, that was the only place where I could stop to take a picture of one of those distance marker...)