The Douaumont charnel house is a burial site for the bones of soldiers killed on the western front near Verdun, who could not be identified. In 1984, on the 70th anniversary of the outbreak of the First World War, François Mitterand and Helmut Kohl stood here hand in hand and declared: "We have reconciled. We have come to an understanding. We have become friends".

The Battle of Verdun, in the north-east of France, is a symbol of the horror of the First World War. Hundreds of thousands of soldiers died between February and December 1916. The museum, founded in 1967, was reopened in the presence of the French President François Hollande and the German Chancellor Angela Merkel on the 100th anniversary of the commemoration of this battle.

The Memorial Notre-Dame-de-Lorette, completed in 2014, lists in the "Ring of Remembrance" (L’Anneau de la Mémoire ) the names of around 600,000 soldiers killed in the northern French region during the First World War. These include soldiers from the British Empire, Germany, France and French colonies in Africa.

This German-French memorial was opened in November 2017 by French President Emmanuel Macron and Federal President Frank-Walter Steinmeier. It complements a national cemetery and a crypt which, since the end of the First World War, have commemorated the victims of a senseless battle of trench warfare over the mountain of the same name in French Alsace.

One of the main war sites of the First World War is the region around the Belgian city of Ypres. The war museum "In Flanders Fields" is located in the Gothic textile halls building, which was rebuilt after the devastating destruction. The name of the museum is the title of a poem by the Canadian military doctor John McCrae, whose friend died in 1915 at Ypres shortly before he wrote it.

Opened in 2005, the museum in Mons, Belgium, does not focus on war equipment or strategies, but on the human being. The display cases contain many personal objects of soldiers and civilians, which give an impression of life during the war and occupation. The region in the northwest of Belgium was a hotly contested site during both world wars.

In the northern Italian town of Rovereto, a war museum, the Castel Dante ossuary and the peace bell commemorate the victims of the First World War. The bell was cast in 1924 from molten cannons of the war opponents Italy and Austria-Hungary. With 100 chimes every evening it recalls the dead of all wars.

The region of Kobarid in present-day Slovenia was also the scene of several battles between Austria-Hungary and Italy during the First World War. The Kobarid Museum (Kobariški Muzej documents the battles on the Isonzo front as well as the everyday warfare of the soldiers on both sides.

Like many others on the Turkish peninsula of Gallipoli, the Çanakkale monument commemorates the battle of the same name between soldiers of the Ottoman Empire and troops from Great Britain, France, Australia and New Zealand. Engraved in stone is a quote attributed to President Atatürk: "There is no difference between the Johnnies and Mehmets. Therefore rest in peace."

In Germany, remembrance of the First World War is mainly decentralized. In almost every community there are monuments for those who died. The "Central Memorial of the Federal Republic of Germany to the Victims of War and Tyranny" has been the Neue Wache in Berlin since 1993. Inside, the bronze sculpture "Mother with Dead Son" was designed by the artist Käthe Kollwitz.

The exhibition "1914/1918 - Not Then, Not Now, Not Ever," shown at the German Reichstag in Berlin, was commissioned to commemorate the end of the First World War on November 11, 1918. The works were created by artists from the 31 countries involved in the conflict. This one is from the German sculptor and installation artist Günther Uecker.

Uecker has been using nails in his art since the 1950s. The Düsseldorf artist's symbolic works, which deal with different political issues, have been featured in different Bundestag exhibitions, including the 1996 installation entitled Fall, in remembrance of the pogrom night in Germany on November 9, 1938. He also designed the Bundestag's Prayer Room in 1998–99.

Each artist was given the same material to create a work for the exhibition: a cube of wood of 30 by 30 by 30 centimeters (12" x 12" x 12") from oak trees that stood in a fiercely disputed section of the front in Alsace. Through discolorations or even leftover war projectiles, traces of the conflict can still be seen in the wood itself. This work is by Bulgarian artist Nedko Solakov.

One of the best-known Bulgarian artists of his generation, Solakov has regularly participated in international exhibitions, such as the Documenta 12 (2007) and Documenta 13 (2012), and the Venice Biennale in 2001, 2003 and 2007. His storytelling works include historical references and touches of humor. Here, he added a few ink spots to the cube of wood to create a work called Dead Warriors.

Austrian avant-garde artist Hermann Nitsch turned the cube of wood into a symbolic butcher's block covered with blood, recalling the brutality of war. World War I caused 20 million deaths and about 23 million military personnel were wounded, making it one of the deadliest conflicts in human history.

Nitsch has long shown his fascination with bloody scenes. His performances in the early 1960s were so provocative that they led to court trials and imprisonment. Although the 80-year-old artist now avoids killing animals during his performances, his "120. Aktion" from 2004 still involved a slaughtered bull, five dead pigs and 600 liters of blood. The blood on the wooden block, however, is paint.

Botha is best known for his sculptures carved out of books. The South African artist often juxtaposes light and movement with dark figures in a state of conflict. The pieces of glass placed around the wooden skeleton in this piece mirror the work's current surroundings, adding new elements and questions to the history of war.

Born in 1974, Botha is one of the youngest artists in the show, along with the Ukrainian Aljoscha and the Turk Cevdet Erek. The exhibition's oldest artist, the Romanian Geta Bratescu, was born in 1926. Interestingly, her installation was the only one to include a video on an iPad. "Variety in the forms of expression was important in the selection of the artists," said curator Mattijs Visser.

The Irish-born American-based artist Sean Scully is renowned for his large abstract paintings. However, for his work entitled The Disappearing Boys, he created a very concrete sculpture. John, Johannes, Jean: three versions of the same name in English, German and French are engraved on a coffin, referring to three of the major European powers at the center of the world conflict.

The curator of the exhibition, Mattijs Visser, said he was fascinated by how the works on show reveal deep connections with the country of origin of the artists. The title of Scully's work can be seen as a reference to those who were abducted, killed and secretly buried during the Troubles in Northern Ireland. These victims were known as the Disappeared.

War and death also have consequences for subsequent generations. The Australian artist Fiona Hall placed a charred cradle on a coffin in her work, entitled Fell. The sculptor was the first to represent Australia in its new pavilion at the Venice Biennale when it opened in May 2015.

Hall is renowned for transforming ordinary, everyday materials into organic forms in her works, giving them historical and contemporary relevance. With the sawdust from her sculpture, she also created a bread that's wrapped in barbed wire. Sawdust was sometimes added to baked goods during World War I to compensate for shortages of flour.

Born in Syria, the painter and sculptor Jean Boghossian is Lebanese and has been living in Brussels since 1975. Since he is also of Armenian descent, the international artist represented the country at the Venice Biennale in 2017 as well as in the "1914/1918 - Not Then, Not Now, Not Ever" exhibition. He split his block of wood into two pieces.

Boghossian is renowned for his experimentation with fire and smoke in his works. In Double World, one side is burnt, representing the losers of the conflict. The sharp edges of the two pieces show how the different camps appear threatening to each other and clash, but the two laser-cut blocks also fit perfectly together, which the artist sees as a symbol of hope.

Tours can be booked to visit the memorial exhibition "1914/1918 - Not Then, Not Now, Not Ever," on show in the German Reichstag building until January 6, 2019. The exhibition will travel to the UN's headquarters in New York in 2019.