One of the most controversial battles of the First World War, Passchendaele continues to divide opinion to this day.

David Lloyd George, Prime Minister at the time of the offensive, described it in his memoirs as 'senseless' and 'one of the greatest disasters of the war'.

But why has it provoked so much debate? Take a look below at some key points from the battle...

  • 1. It's impossible to know the exact number of casualties on either side. Estimates of British casualties have ranged from 200,000 to 448,614, while German losses are believed to be between 260,400 and 400,000.
  • 2. Empire troops paid a heavy price. Around 36,000 Australians, 3,500 New Zealanders and 16,000 Canadians were killed, the latter of which were lost in the closing stages of the battle.
  • 3. This is despite Field Marshal Douglas Haig being under constant pressure to halt the attack, with many historians having since questioned why he allowed his soldiers to continue it. He has been nicknamed "Butcher Haig", with the Canadian War Museum commenting that "his epic but costly offensives at the Somme (1916) and Passchendaele (1917) have become nearly synonymous with the carnage and futility of First World War battles."
  • 4. As a result, Passchendaele's Tyne Cot cemetery is the largest for Commonwealth forces in the world, for any war.
Tyne Cot Commonwealth War Graves Cemetery
The Tyne Cot cemetery at Passchendaele. Picture: Gary Blakeley
  • 5. And despite these losses, barely five miles of territory was gained - after three months of intense fighting.
  • 6. Troops, horses and tanks literally disappeared into a sea of mud, caused by shelling and flooding. The battlefield was situated in a low-lying area reclaimed from marshy lands through an elaborate drainage system, leaving it vulnerable and easily destroyed by shellfire.
  • 7. Millions of unexploded munitions remain buried in the soil at Passchendaele to this day. So much so, that every year there's an 'iron harvest', where ordnance, barbed wire, shrapnel, bullets and other relics of war are collected by Belgian farmers after ploughing their fields and left for disposal.
Iron Harvest
A German First World War artillery shell left beside a Belgian field for disposal
  • 8. That's because 3,000 guns bombarded German lines in 10 days leading up to the attack, with over 4.25 million shells fired.
  • 9. Donkeys were led by lions. Or mules, rather. The animals were used to carry shells through the mud to the frontline.
  • 10. The name 'Passchendaele' only came into use after the battle. At the time it was called Third Ypres, or the Third Battle of Ypres, because there had been two prior battles fought in the same spot in 1914 and 1915.
  • 11. 90,000 bodies were never identified - and 42,000 never recovered.

If you'd like to find out about commemorations to mark the centenary of the start of the battle, you can take a look here.