More than 20,000 people, many of them Canadians, gathered for a ceremony in northern France on Sunday to remember a World War I battle that left an indelible mark on Canada's national identity - 100 years after it happened.

On a balmy spring day, with the thermometer pushing 23 degrees Celsius (74 degrees Farenheit), Canadian Prime Minister Justin Trudeau led a procession of dignitaries, including French President Francois Hollande and British royalty, through the solemn commemoration of the century-old battle at Vimy Ridge.

"They were, most of them, young men in their late teens, in their early 20s," Trudeau said at the ceremony. "Going as far as sacrificing their lives, these men both ordinary and extraordinary of the British dominion fought for the first time as citizens of a single and same country...side by side here in Vimy."

Some 3,600 Canadian soldiers died and more than 7,000 were injured during the three-day battle. Largely because of its military achievement in northern France, the North American country was a separate signatory to the treaty that ended World War I.

"In this sense, Canada was born there," Trudeau said.

Amid sleet and snow, Canadian volunteers managed on April 9, 1917 to push back German forces from a long-held strategic post. To protect soldiers from shelling, they, along with New Zealand forces, built miles of tunnels - one of the war's great engineering feats allowing troops to pop up quickly into their positions.

Although the battle is not considered among the largest during World War I, it played a key part in establishing Canada's role in the conflict and eventually symbolizing the nation's founding events.

Canadian troopers advanced in the muddied battlefield to push back German forces during World War I from a strategic position

Canada's defining moment

The battle marked the first time four military divisions from Canada had fought together as a unit dubbed the Canadian Corps.

"It made the Canadian Corps think it could do anything. It made the soldiers believe that they were really good soldiers, better than anybody else. They had done something that the British and French were not able to do," said Canadian military historian Jack Granatstein.

Printed on the back of Canada's $20 bill, the memorial at Vimy is considered one of the finest World War I memorials in Europe, paying homage to the 11,285 soldiers killed or "missing, presumed dead" during the battle.

Britain's Prince Charles attended the commemoration with his sons, Princes William and Harry, who dropped boots symbolizing the dead soldiers and ceramic poppies at the grand war memorial that marks the site of the battle.

"Their sacrifice must inspire us to do everything to avoid that senseless losses happen again," Charles said of the Canadians who lost their lives in France. "Let's renew our commitment to remember their heroism in the face of suffering and fear."

World War I in color Record of devastation During the First World War, photography was mainly seen as a means of spreading propaganda and of serving military interests. Depicted here is the view over the River Maas and the devastated city of Verdun. In fall of 1916, up to 400 members of the German army were involved in aerial photography. Some civilians also took photographs documenting moments of terror - and of joy.

World War I in color The first sunset after the war The book "The First World War in Colour,“ edited by Peter Walther, presents more than 320 color photographs which originally came from archives in Europe, the US and Australia. They document events during the war, ranging from the mobilization in 1914 to the victory celebration in London, New York, and at the Arc de Triomphe in Paris on July 14, 1919.

World War I in color The novelty of color The first color photographs were produced with the so-called autochrome technique which its inventors, the Lumière brothers, had patented in 1904. Tiny particles serve as color filters, bearing a small resemblance both to paintings and to modern digital photography. This photograph depicts the French blimp "Alsace," which was shot down on October 3, 1915.

World War I in color At the front Because the autochrome technique required long exposure times, the photographs taken near the front were often carefully posed. Nevertheless, we gain insight into the daily lives of people and the horrors they had to deal with. Here, a motorized gun-carriage with a cannon used for air defense is pictured in Verdun in 1916.

World War I in color Appeal for donations This picture, shot by the American Committee for Devastated France (1917-24) in 1918, depicts an ammunition depot in France. The committee's aim was to alleviate the enormous suffering of French war refugees. The photographs were taken to help the Americans visualize what was going on in Europe - and to persuade them to make donations.

World War I in color Private photos for the family For the first time, not only the government but also private individuals were able to take photographs during World War I. As a result, not only propaganda photos, but also soldiers' personal impressions of the front and everyday life remain. In the French army, taking photos was officially forbidden, but the rule wasn't strictly enforced. Here, a French soldier is posing in a concrete dugout.

World War I in color Aerial warfare For the first time in history, aerial warfare came into play in the First World War. Pictured here is a French war plane. At the beginning of the war, the French and Britons together possessed as many planes as the Germans. Thanks to the air surveillance carried out by the Royal Flying Corps, the Germans could be stopped at the Battle of the Marne in 1914.

World War I in color Rolling tanks The first tanks were used by the Britons in the fall of 1916, in order to break open the gridlocked fronts. This British tank was photographed in Péronne near Amiens. By 1918, the Allies were able to acquire up to 6,000 tanks. At first, Germany underestimated the powerful new weapon. It wasn't until the spring of 1918 that the Germans developed and implemented a tank of their own, the A7V.

World War I in color The speed of war A whole range of new weapons was developed during the First World War, from war planes to tanks and poison gas. The increased use of motorized vehicles made the front more dangerous, but it also meant that injured soldiers could be transported relatively quickly to medical facilities - for example with this British ambulance in 1914.

World War I in color Art and evidence The photo pioneers were able to preserve their photo chrome plates over four years of war. Their works are not only evidence of the Great War, but also impressive works of art which deserve to be rediscovered. Peter Walther's "The First World War in Colour" was published both English and German by TASCHEN. Author: Sarah Judith Hofmann / ad



ls,bik/se (AP, AFP)