A drone's-eye view of the preserved World War I battlefield at the Beaumont-Hamel Newfoundland Monument in Beaumont-Hamel, France, on June 10, 2016. The preserved trenches and craters are part of the grounds on which the Newfoundland regiment made their unsuccessful attack on July 1, 1916, the opening day of the Battle of the Somme. #

A German fortification sits overgrown in the forest of Argonne, France, in May of 1998. The Battle of the Argonne Forest was part of the Meuse-Argonne Offensive planned by General Ferdinand Foch. General John Pershing led the American Expeditionary Forces (AEF) at the Battle of the Argonne Forest, while General Henri Gouraud led the French Fourth Army. U.S. casualties at the Battle of Argonne Forest totaled 117,000. The French lost 70,000 men and the Germans lost 100,000. #

A piece of barbed wire from World War I stands on the site of the former village of Bezonvaux on August 27, 2014, near Verdun, France. Bezonvaux, like a host of other villages in the region, was obliterated during the intense artillery and trench warfare between the German and French armies during the Battle of Verdun in 1916, and was never rebuilt. #

Stone crosses marking the graves of German soldiers are overtaken by time and and the growing trunk of a tree in Hooglede German Military Cemetery on August 4, 2014, in Hooglede, Belgium. #

An old World War I German bunker stands in Spincourt forest on August 27, 2014, near Verdun, France. At least half a dozen of the bunkers still stand in the forest in an area where the German army maintained a hospital, rail connections, and command posts during the Battle of Verdun. #

This aerial picture shows the remaining gate of the destroyed Chateau de Soupir, near the famed "Chemin des Dames" (Ladies' Path) along which World War I battles were fought, photographed on March 25, 2017. #

"These are some of our Marines buried here," said U.S. Marine Sergeant Major Darrell Carver of the 6th Marine Regiment as he walked among the graves of U.S. soldiers, most of them killed in the World War I Battle of Belleau Wood, during a ceremony to commemorate the 100th anniversary of the battle on Memorial Day at the Aisne-Marne American Cemetery on May 27, 2018, near Chateau-Thierry, France. Nearly 100 years before U.S. soldiers, including marines from the 6th Regiment, repelled repeated assaults from a German advance at Belleau Wood only 60 miles from Paris. The U.S. suffered approximately 10,000 casualties in the month-long battle. Today the Battle of Belleau Wood is central to the lore of U.S. Marines. #

The remains of the Chateau de la Hutte in Ploegsteert, Belgium, photographed on November 21, 2014. The chateau, due to its high position, served as an observation post for the British artillery, but soon afterwards was destroyed by German artillery. The cellars would serve as a shelter for a great part of the war and Canadian soldiers soon nicknamed it "Henessy Chateau" after the owner. #

A tree grows in the World War I London trench at Douaumont near Verdun, France, on March 30, 2014. After the recapture of Fort Douaumont and Fort Vaux by French troops in late 1916, this trench was built to join the town of Belleville with both Fort Douaumont and the ruined town of Douaumont in order to deliver supplies, relieve troops, and allow for hospital evacuation. #

A corridor runs through a section of Fort Douaumont in Douaumont, France, on September 3, 2013. Built from 1885 to 1913, Fort Douaumont is the largest and highest fort of the ring of 19 large defensive forts, which protected the city of Verdun during World War I. #

This aerial picture, taken on March 25, 2017, shows the forest of the plateau de Californie near Craonne, where shell holes and trenches can still be seen, near the famed "Chemin des Dames." #

An unexploded World War I shell sits in a field near Auchonvilliers, France, in November of 2013. The iron harvest is the annual "harvest" of unexploded ordnance, barbed wire, shrapnel, bullets, and shells collected by Belgian and French farmers after plowing their fields along the Western Front battlefield sites. It is estimated that, for every square meter of territory on the front from the coast to the Swiss border, a ton of explosives fell. One shell in every four did not detonate and buried itself on impact in the mud. Most of the iron harvest found by farmers in Belgium during the spring-planting and autumn-plowing seasons is collected and carefully placed around field edges, where it is regularly gathered by the Belgian army for disposal by controlled detonation. #

Sunlight highlights craters created by artillery bombardments during the fierce Battle of Les Eparges Hill during World War I on August 26, 2014, near Verdun, France. The German and French armies fought a vicious battle for control of the strategically significant hill in 1915, which preceded the much larger Battle of Verdun in 1916. #

A German World War I bunker, named the "Devil's Bunker," sits upon a hill in Cuisy, France, on March 24, 2017. American troops in the Meuse-Argonne region battled constantly for the high ground, which provided a vantage point against the enemy. #

A barbed-wire fence and the landscape, as seen from a gun position inside of a World War I bunker in Belgium on February 28, 2014. Bunkers and trenches, many very well preserved, can still be seen across the landscape in Flanders Fields. #

Early-morning sunlight at Tyne Cot Commonwealth War Graves Commission cemetery on March 25, 2014, in Passchendaele, Belgium. Tyne Cot is the largest commonwealth war cemetery in the world. There are 11,956 commonwealth servicemembers from World War I buried or commemorated here. #

The skeleton of a church stands at the site once occupied by the village of Ornes on August 27, 2014, near Verdun, France. Ornes, like a host of other villages in the region, was obliterated during the intense artillery and trench warfare between the German and French armies during the Battle of Verdun in 1916, and was never rebuilt. #

A steel machine-gun turret overlooks the Woëvre Plain from the top of Fort Douamont on August 27, 2014, near Verdun, France. Fort Douamont was one of a string of French forts built along the Cotes de Meuse hilltop range, which became a focal point of bitter fighting between the German and French armies during the World War I Battle of Verdun in 1916. #

The setting sun illuminates the sculpture of the "Brooding Soldier," commemorating the Canadian First Division's participation in the Second Battle of Ypres of World War I, on August 2, 2014, in Saint Julien, Belgium. #