By Phil Mercer BBC correspondent in Sydney

Services have been held across Australia to mark Anzac Day.

It is held on 25 April every year and celebrates the legend that emerged from the bloody failure of Gallipoli, where 8,000 Australian soldiers died alongside British, French and New Zealander colleagues, in one of the darkest episodes of World War I.

For many Australians, the conflict fought out on the beaches on Turkey's rugged Aegean coastline in 1915 forged the fledgling nation's identity.

Allied casualties at Gallipoli

Britain 120,000 France 27,000 Australia 26,000 (8,000 dead) New Zealand 7,500

Doctor Frank Bongiorno from the Royal Australian National University believes that at Gallipoli the former colony finally achieved nationhood.

Coming of age

"Many Australians had come to recognise 25 April 1915 as the day their young Commonwealth had come of age," he said.

Much of the literature devoted to the campaign says it was a defining moment in history.

"At Gallipoli men from all backgrounds created the essence of what it means to be Australian," wrote one observer; "courage under fire, grace under pressure and giving hand to a mate."

Lieutenant Colonel AH White was killed within metres of the Australian trench after leading his men into battle.

There is only one man still alive who survived Gallipoli

"Boys, you have 10 minutes to live and I am going to lead you," were his last heroic words.

Francis Twisleton landed at Gallipoli in May 1915. In private letters, the soldier - or digger - described the nightmare that unfolded around him.

"I felt as though I could scrape the smell of dead men out of my mouth and throat and stomach in chunks," he wrote.

A need to remember

The guardian of the Anzac (Australian and New Zealand Army Corps) tradition is the Returned and Services League (RSL), a powerful organisation representing 222,000 former servicemen and women across Australia.

The state president of the RSL in New South Wales, 74-year-old Rusty Priest, says Australians must never forget the sacrifices made for them.

"People need to have constant reminders of the horror of war," he told the BBC. "Military service is a debt that can never be repaid."

Trenches provided little protection from heavy gunfire

Last year 23,400 people took part in the parade through Sydney as more than a quarter of a million spectators looked on.

The RSL expects even more people to line the streets this year. Other marches pass through almost every major town and city in Australia.

But with only 17 surviving WW I veterans still alive in Australia, including a solitary survivor from Gallipoli, there is a concern that the country's enthusiasm for the day of remembrance will wane as their numbers decline.

Rusty Priest believes that will never happen. "Anzac Day gains more importance as the years go by," he insisted.

The young, he said, have been engendered with a renewed passion and respect for Anzac Day.

The rallies attract veterans from various conflicts, from WW I to Vietnam, as well as peacekeepers who have served in Bougainville and East Timor.

Thirty-four-year old Chris Dawes, who was an electrical weapons expert for the Australian navy in the Gulf War, will march in Adelaide.

"You get a good burst of pride realising what you did has been recognised and respected by the people," said the veteran of a decade in the armed forces.

Not all Australians feel this sense of pride.

Historian Pauline Kurby - who took part in anti-war demonstrations in Melbourne and Sydney during the Vietnam conflict in the late 60s and early 70s - told BBC News Online she is ambivalent towards the Anzac tradition:

"Even though we're honouring the dead, I am suspicious of this glorification of war," she said.