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7 year oldReporters from around the world were there too, gently questioning some of those who came.
The people of London and visitors to the city came together to remember the people who lost their lives in Wednesday's attack.
The word "solidarity" was heard over and over again.
Candles were laid on the ground and on the steps leading to the National Gallery, then lit in memory of those who died.
German-born Michaela Thomas, who has lived in Poplar for decades, came to take part in the vigil, but her husband did not feel safe enough to join her.
She said she was there because she did not want terrorism to stop her living her life.
Her view was echoed by almost everyone I spoke to around the square.
Sister Petronia, a nun from Hackney, put on her London 2012 Gamesmaker jacket to attend.
"I feel everybody in London is the heart of London beating," she said.
"When something like this happens, those of us who live here feel the pain.
"People want to come together and express solidarity, and express their desire for peace."
At the front of the crowd, Donnelly Devereaux and her daughter Mary-Katherine Caestecker, both from Chicago, waited for the ceremony to begin.
"We're visiting the city and we wanted to come tonight to show our support, particularly as one of the people who died, Kurt Cochran, was from the US," Mrs Devereaux said.
"It's so much more calm here than it would be at home. Everyone's so calm and collected on the tube, and here in the square tonight."
As the bells of St Martin-in-the-Fields chimed, the crowds fell silent.
Even the rumble of the police helicopters dimmed while those gathered here paused to think about yesterday's events.
Some filmed the scene on their phones, some cast glances across the crowds, but the focus was on three candles on the steps leading up to the National Gallery, above which MPs, religious figures and others stood in a line to pay their respects.
As Met Police Acting Commissioner Craig Mackey, Home Secretary Amber Rudd and London Mayor Sadiq Khan addressed the crowds, bursts of applause broke out and people around me cheered when Mr Khan told them: "Londoners will never be cowed by terrorism".
The minute's silence was impeccably observed - no chatter in the crowd, no phones going off, just people bowing their heads and closing their eyes to remember what happened about half a mile away.
The scent of flowers hung in the air from the tributes people had brought with them.
As the bells of St Martin-in-the-Fields chimed quarter past the hour, and a siren could be heard in the distance.
As the ceremony ended people moved across the square to light candles, I spoke to Danny Lyne, a teacher from the East End of London, who came here after work.
"What happened yesterday has been in my head ever since I found out," he said.
"I remember what happened 12 years ago, on 7/7, and this has brought it all back.
"I think it's important to pay respect to those who lost their lives this time, and to give respect to the police - the Met Police in particular don't often get that."
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