(CNN)The remains of more than 200 German soldiers who were buried alive in a tunnel in northeastern France during the World War I will not be recovered.
The German government has instead decided to declare the burial site a war memorial and put it under state protection.
Germany's war grave commission, the Volksbund, and the French government announced the decision at the Caverne du Dragon museum in northeastern France on Friday afternoon.
"Rescue efforts to reach the remains in 2021 and 2022 had proven very difficult," a spokeswoman for the Volksbund told CNN on Friday, adding that there had been "several attempts" to open the "very deep and very long" tunnel, which is located in a nature reserve with "sandy ground still contaminated with ammunition."
Although the Franco-German team managed to see as far as 64 meters (210 feet) down the tunnel, they "did not find any remains," the spokesperson said.
Many WWI battles took place between the French armed forces and German troops positioned on the Chemin des Dames, or "Lady's Way," a crest between two valleys.
On May 4, 1917, during one of the biggest battles of the war, the French army was firing on German soldiers with heavy artillery. An artillery shell hit the entrance of the Winterberg tunnel on the Chemin des Dames, according to the Volksbund.
Some of the German troops, from the 111th Baden Reserve Infantry Regiment, fled further into the tunnel, where stored ammunition had exploded and toxic fumes were being released.