VIMY (AFP) - Canadian Prime Minister Justin Trudeau was to lead the commemorations on Sunday (April 9) for the 100th anniversary of the Battle of Vimy Ridge in France, considered a founding moment in his nation's history.

Mr Trudeau was to be joined at a ceremony at the Canadian National Vimy Memorial by French President Francois Hollande and Britain's Prince Charles and his sons Princes William and Harry.

Around 20,000 Canadians made the journey to the memorial in northern France to mark the centenary of the battle which was one of the defining moments of World War I.

Canadian troops fought under Canadian command as a united force for the first time there, defeating the German forces in just three days, although they paid a heavy price with 3,600 Canadians killed and 7,000 wounded.

"The Battle of Vimy Ridge was a turning point in the First World War and for Canada, when Canadians acted - and fought - as one," Mr Trudeau said ahead of the commemorations.

"At Vimy Ridge, we will mark this great victory, and pay tribute to every Canadian who answered the call to serve."

The battle began early on April 9, 1917 and was part of a larger British-led offensive that included Australian soldiers, known as the Battle of Arras, which was a diversionary tactic to assist a major French attack further south.

It was the first time that four military divisions from Canada fought together as the Canadian Corps.

'Shaking off colonial rule'

In bright spring sunshine, the crowd at the memorial site was a sea of red t-shirts, many of them showing the Canadian flag.

Mr Ken Piggott, 54, a retired army captain from Yarmouth, Nova Scotia, who was wearing full military uniform and a row of medals, said: "Vimy is important because it was the first time that Canadians fought together under Canadian command. It was an important step in shaking off British colonial rule.

"For that reason, it is a huge source of pride for me." .

Many of the crowd were teenagers like Mr Jacob Woodgate, 17, from Thunder Bay, Ontario. He had come in a group from Canada, many visiting Europe for the first time.

He said: "It's the most amazing feeling when you walk up to the Vimy site and you see the bomb craters that are still here. It really hits you when you think that some of the soldiers who died were my age."

Starting the commemorations earlier on Sunday, Mr Trudeau and Mr Hollande laid the final red metal discs to form a giant poppy in the central square of the town of Arras, called Heroes' Square.

The centre of the poppy is formed by a newly-unveiled sculpture of pairs of soldiers' feet by New Zealand artist Helen Pollock.

A vast warren of tunnels dug by New Zealand forces was crucial to the victory at Vimy allowing the Canadians to take the German troops by surprise.

While many Canadians consider the victory at Vimy a significant step in their nation's development, some Canadian historians have debunked the state's official view of its significance.

Mr Michael Boire of the Royal Military College in Kingston, Ontario, said it was "pure mythology".

It was neither decisive for the war's outcome "nor the most fundamental" of the battles fought by Canadians during the conflict, Mr Boire said.

Canada would gain political quasi-autonomy only in 1931.

"The importance given to the Battle of Vimy is a post-war mythological construction," he said, an "invention" dating back only to 1967, the year of Canada's centennial and the battle's 50th anniversary.

Mr Tim Cook, of the Canadian War Museum in Ottawa, said however its importance could not be underestimated.

"Many historians and writers consider the Canadian victory at Vimy a defining moment for Canada, when the country emerged from under the shadow of Britain and felt capable of greatness," he said.

Mr Trudeau, Mr Hollande and Prince Charles will each give speeches and lay wreaths during the ceremony.

Princes William and Harry - who have each served in the armed forces - will lay a pair of boots, among thousands that will be placed at the site by Canadian and French youths to represent the Canadians killed in the battle.