PARIS (AP) — Canadian Prime Minister Justin Trudeau is among the dignitaries commemorating the centenary of the World War I battle of Vimy, in northern France.

About 20,000 people, including many Canadians, are expected to attend the ceremony Sunday, including French President Francois Hollande and British royals Princes Charles, William and Harry.

On April 9, 1917, the Canadians succeeded in taking the German's strategic post on Vimy Ridge — where past British and French attempts had failed. The move cost 3,600 dead and over 7,000 injured in three days.

The battle has become an important part of Canada's national identity, symbolizing the shift from a former British colony to a nation on its own.

The Vimy memorial also pays tribute to the 11,285 Canadian soldiers who died in France and have no known graves.