Top envoys of former World War I enemy nations converged on Ypres in western Belgium Monday for a second day of commemorations marking Passchendaele, where at least 460,000 German and British-allied soldiers died in 1917.

The Battle of Passchendaele, also known as the Third Battle of Ypres, lasted from July 31 to December 31 of that year amid heavy rainfalls and massive shelling that shattered the small town and the surrounding countryside.

Monday's commemoration venue was Tyne Cot Cemetery, the largest graveyard for British Commonwealth forces in the world.

That ceremony, jointly organized by British and [local] Belgian authorities, was attended by German Foreign Minister Sigmar Gabriel, Britain's Prince William and his wife Kate, and the Belgium royal pair Philippe and Mathilde.

'Never again'

"Diplomacy must never again fail as it did in 1914," said Germany's Gabriel.

"There must never again be war in the middle of Europe, and never again must the youth of our continent be slaughtered," he stressed, adding that a united Europe was a "project of peace" and "our future."

In coming months, remembrance ceremonies will be held especially for Scottish, Australian and New Zealand soldiers who also fell in combat.

Visiting Ypres, Welshman Peter Carter-Jones said the commemorations recalled "those thousands of young men who died here so we can live in freedom.

"That is what it is about," he said.

Similar in scale

Although not as well known as the famous battles on the Somme and at Verdun, the Battle of Passchendaele was similar in scale. In his memoirs of the First World War, British Prime Minister David Lloyd George wrote that Passchendaele would always rank among "the most gigantic, tenacious, grim, futile and bloody" fights ever waged.

A bulge in the frontline

World War I began in August 1914 with German troops invading neutral Belgium and Luxembourg in an effort to bypass the heavily fortified French-German border and encircle Paris by marching down from the north. The Allies halted their advances in western Belgium in the First Battle of Ypres in November 1914, and entrenched fronts were established. The war of attrition was on.

German forces made another attempt in 1915 to take the biggest city in the region in the Second Battle of Ypres. That battle was notable because it was the first time that Germany used poison gas on the Western Front in the war and the first time that a former colonial force (the First Canadian Division) defeated a European power in Europe. The stalemate continued - around 60 kilometers (37 miles) from Dunkirk and 250 kilometers (155 miles) from Paris.

The area around Ypres was an Allied "salient," or bulge, into German-held territory, which made it costly to defend. Allied forces decided to launch an offensive of their own in late July 1917 with the aim of driving Central Forces troops back and seizing the strategically important hills in the region. That move led to the Third Battle of Ypres, a.k.a. the Battle of Passchendaele.

What the Allies didn't plan on was the weather.

The campaign of the mud

Skies were overcast when British forces began the offensive at 4 a.m. on the morning of July 31, 1917, and that was an omen. While some army groups were able to advance by around four kilometers, other brigades were driven back and suffered losses of up to 70 percent.

That area of Belgium in August 1917 saw more than four times the amount of rainfall than it had in August 1914, and that made it impossible for troops on either side to achieve any decisive progress. Pictures of the battlefields show a seemingly endless terrain of mud interrupted by the odd charred tree with its top blown off. Lloyd George would even term Passchendaele "the campaign of the mud."

Over the five months from July 31 to the end of 1917, there were repeated cycles of attacks and counter-attacks in which territorial gains were measured in meters, not miles. Passchendaele was at the center of the carnage. Aerial photographs of the town before and after the battle suggest that it was nearly completely obliterated.

In the end the territorial gains were as minimal as the loss of life was huge. Estimates of casualties differ significantly. The most conservative figures put the number of German dead at 217,000 and those of the Allies at a quarter of a million. But far more probably died in these particular fields of Flanders.

Was it worth it?

Just as there is no definitive number of the dead, there is no accepted historical consensus about whether the Battle of Passchendaele was good for anything at all.

Defenders of the attempted British-led offensive and in particular of British commander Douglas Haig argue that the battle forced the Germans to commit troops to holding the line in Flanders who could have been deployed elsewhere. Although Allied casualties were higher, the German army could far less afford to lose men, and so the Battle of Passchendaele may have helped convince the German High Command that the war couldn't be won without what would ultimately prove to be a disastrous final offensive.

On the other hand, it can be argued that the course of the war was decided completely elsewhere in 1917 with Germany's decision to engage in unlimited submarine warfare, the sinking of the Lusitania and the United States' entry into the conflict. And the numbers of dead in this battle horrify even today.

Summing up the import of the Battles of Passchendaele, the Somme and Verdun, Lloyd George wrote the following.

"None of them attained the object for which they were fought. In each case it was obvious early in the struggle to every one who watched its course - except to those who were responsible for the strategic plan that wrought the grisly tragedy - that the goal would not be reached. Taken together they were responsible for the slaughter or mutilation of between two and three million of brave men."

The English poet and former soldier Siegfried Sassoon had a more concise evaluation. In a poem written from the point-of-view of a fallen soldier, Sassoon simply said: "I died in hell (They called it Passchendaele)."