Where

Northeastern France, from the Somme to the Vosges. Scattered patches lie across eleven departments, with the heaviest concentration around Verdun.

What it is

"Completely destroyed. Damage to property: 100%. Damage to agriculture: 100%. Impossible to clean up. Human life impossible."

Those words come from the official classification the French government gave the area after the First World War. The zone was given its own name: zone rouge.

How big

More than 1,200 square kilometres, about a fifth of the province of Antwerp. The soil there is no worse than elsewhere; the zone is so large because fighting went on for years. France alone is estimated to have lost seven percent of its territory to total destruction.

What lies there

Shells, millions of them, and not all of them exploded. Among them lie poison gas shells, rifle grenades, human and animal remains, and a soil saturated with lead, mercury, chlorine and arsenic.

In the worst stretches, researchers found up to three hundred shells per hectare in the top fifteen centimetres of soil in 2005 and 2006. At Verdun, in a spot called Place à Gaz, arsenic levels run as high as 176 grams per kilogram: eighteen percent of the soil.

Who lives there

Almost no one lives there. Nine villages were never rebuilt. Fleury-devant-Douaumont still appears on the map as a municipality, but no one lives there anymore; it is a name and a few foundations among the trees. France calls such places villages morts pour la France.

Much of the land is owned by the state. After the law of 1919, the government could buy up plots that could not be restored quickly or at all, with compensation for the owners or their heirs. Some hectares are still off-limits.

How long still

Every year, more munitions are cleared. The Sécurité Civile, the service responsible for the zone, estimates that at the current pace it will take another three hundred to seven hundred years to clear everything.

In some places no one needs to search: there they wait for the next rain shower to bring something else to the surface.

Why it remains

Clearing is dangerous, expensive and slow. The ground has five problems at once: explosives, chemicals, remains, collapsing trenches, and a forest that has grown over it all and holds everything in place.

The area has also become a monument. There are crosses and walking routes; every year there is a commemoration. The black pines that Austria sent after the war as reparations are still standing.

What strikes me most about the zone rouge is the honesty of that classification. Governments are usually bad at admitting that something will never be right again. Here it was set down in black and white, in 1919, and a hundred years later it is still there.

"Back to nature" sounds like recovery. It is an armistice with the soil: the forest may stay, as long as no one builds anything on it. The war is over, even if the land does not know it yet.

Source: Zone rouge — Wikipedia, with references to, among others, BBC Travel and National Geographic.