The campaign on Turkey's Gallipoli peninsula has resonated through generations, which have mourned thousands of soldiers from the Australian and New Zealand Army Corps (ANZAC) cut down by machinegun and artillery fire as they struggled ashore on a narrow beach.
The fighting would eventually claim more than 130,000 lives, 87,000 of them on the Ottoman side.
Australian Prime Minister Tony Abbott told the crowd, many of whom spent the cold night in their sleeping bags to secure a spot at the crowded grounds, about the lives lost during the campaign, which helped forge Australia's identity.
"Like every generation since, we are here on Gallipoli, because we believe that the Anzacs represented Australians at our best," he said.
"It's the perseverance of those who scaled the cliffs under a rain of fire. It's the compassion of the nurses who attended to the thousands of wounded.
"And it's the greatest love anyone can have: the readiness to lay down your life for your friend."
Gallipoli was the first time that soldiers from Australia and New Zealand fought under their own flags and is seared in the national consciousness as a point where their nations came of age, emerging from the shadow of the British empire.
The area has become a site of pilgrimage for visitors from the two countries, who honour their fallen in graveyards halfway around the world on ANZAC Day each year.
This year is set to be the largest ever commemoration.
The thousands at Gallipoli were marking the anniversary amid heightened security, following a police raid in the Australian city of Melbourne last week that targeted an alleged plot to attack local celebrations there.
WATCH SBS Europe Correspondent in Gallipoli ahead of the Anzac Day dawn ceremonies
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