From the gloom they come, stepping from the shadows at a steady pace. Heads bowed in the pre-dawn air, backs bent with age or weariness or the weight of sleeping children.

The lights are bright in Martin Place. Plastic chairs are marshalled into rows as people stand to attention along metal barricades, waiting and watching for the dawn.

Among them is Noel Darr, 76, a retired airman who couldn't sleep so he showered and shaved and walked here in uniform. As the big clock behind him ticks towards 4.30am, he remembers the wounded and "messed up" men he helped fly home from Vietnam.

Each tick brings them closer. His eyes are bleary. His hands twist at a black umbrella handle.

"When you're young you put it in the back of your mind but as you get older you tend to get emotional," he says.

The dawn service. More dark than dawn, in truth, the skies illuminated by office lights and building sites. In the long hours before the service starts, car horns blare and 20-somethings stagger home from late-night revelries.

Some pass by Justin King, 29 years old but already a veteran of the Afghanistan War. He chews gum for breakfast and fiddles with the glossy order of service.

"It's not a nervous feeling waiting here," he says. "It's daunting. A sadness. An eerie feeling."

The crowd builds back from the Cenotaph to Macquarie Street and spills out into George Street, where people gather around big screens. They come in coats and scarves, shuffling their feet and crossing their arms against the expected cold, but it's a mild morning with a light breeze.

It's the biggest crowd in years, organisers reckon. Just how many is anyone's guess. Perhaps more than the 8141 Australian men who died at Gallipoli, 99 years earlier.

Their names flicker on big screens in Martin Place: Robert Yuill, 7th battalion AIF, died April 24, 1915, aged 19; Clarence Dodds, 14th battalion AIF, died April 30, 1915, aged 25, "my well loved laddie waiting for mother".

An Australian Army band musician sings softly Abide With Me, her words fading into the darkness before dawn. "Swift to its close ebbs out life's little day. Earth's joys grow dim, its glories pass away."

Heads rest on shoulders, hands on hearts, as the service begins. A child falls asleep in her dad's arms. A mother rubs her red eyes. Lieutenant General Ken Gillespie wonders what the troops might have felt so many years ago. "Was it uncertainty? Fear? Exhilaration? Calm?"

He quotes the words of a soldier there, writing at the end of a day "which I pray to God I should never have to visit again". But with dawn came another day worse still.

It is still dark this morning when the spotlights are extinguished and the Last Post plays. It is only with the lights out that you can see the leaden sky.