Sixty-five years ago this month, the first death camp in western Europe was liberated by Canadian soldiers. The horrors they uncovered shocked the world.

But with the passing of time, memories have faded. There are growing numbers today who question whether the Holocaust really happened.

Inexplicably, there have always been dissenters. In 2000, a British court ruled that historian David Irving deliberately manipulated evidence to conceal the extermination of Europe's Jews. In Canada, Ernst Zundel published books and pamphlets with a similar theme. He was deported to Germany in 2005 and sentenced to five years in prison for inciting racial hatred.

But those were the work of isolated cranks. Their claims were swiftly rejected, often with the force of law.

Something much uglier is occurring in parts of Europe and the Middle East. An ultra-nationalist party recently formed in the European Parliament. Campaigning on a platform of identity, tradition and sovereignty, party officials have flatly denied the Holocaust.

The same is true in some Middle East countries. The president of Iran, Mahmoud Ahmadinejad, has called the extermination of the Jews "a fabricated legend."

Few of these doubters had personal experience of the Holocaust. Perhaps that explains some of the skepticism, though not all of it.

But if the passage of time is to blame, all the more reason for those who witnessed this tragedy to speak out. Canadian soldiers, better than most, can do so.

In the closing days of the Second World War, our armed forces marched deep into German-occupied territory. The scenes they encountered have no parallel in human history.

Their ordeal began in October 1944, when units of the First Canadian Army liberated the Vught concentration camp in Holland.

Vught was built as a deportation centre. Some 12,000 Dutch and Belgian Jews, including 2,000 children, were housed there before being sent east to their deaths. Hundreds more were executed on the spot.

When Canadian soldiers arrived, most of the prisoners had already been killed or taken away. But the gallows, shooting pits and crematorium left no doubt what happened there. It was only the beginning.

Advancing from the west, Canadian, British and American forces came upon a string of death camps. Their names are a synonym for horror: Bergen-Belsen, Buchenwald, Mauthausen, Dachau. On the eastern front, the Russian army liberated Sobibor, Treblinka, Ravensbrück and Auschwitz.

Even then, the German SS and the Gestapo would not give up their prisoners. Those still alive were marched to the rear so time could be found for their execution.

When the Allies set up field hospitals to treat survivors, they were bombed from the air. Apparently killing Jews was more important than defending the homeland.

The final death count took several decades to verify. Where possible, camp administrators destroyed records and concealed evidence.

Nevertheless, at least six million helpless victims are known to have been liquidated. About one and a half million were children.

And of course, almost all were Jews. By the end of the war, two out of every three Jews in Europe were dead. Close to half the Jewish race worldwide had perished. Millions of other victims -- disabled, Roma, homosexuals were also killed.

None of this is conjecture. The broad facts are indisputable.

Anyone in doubt can visit Vimy Place in Ottawa. The Canadian War Museum is there.

Among its archives are the reports of men and women with no reason to lie: Soldiers, journalists, photographers. What they saw, and never forgot, was the apparatus of mass murder.

Holocaust denial is a slander on history. It is also, in a small way, a slander on the thousands of Canadians who encountered evil and understood what they saw.