Under grey skies on a late spring day, mourners held up signs such as "Love for all, hatred for none" and "N.Ireland supports London," as the British flag flew at half-mast on the bridge, a monument of national endurance.
"There's nothing better to do than come here and pay respect to such an awful situation, you know, just to come out and be with everybody in a time where everybody needs to be together," said Matthew Chamberlain, 21, from south London.
"It just felt like the right thing to do."
Sniffer dogs roamed the area before the brief vigil, and police, armed and unarmed, maintained a high-profile presence.
Muslim groups were prominent among the several hundred mourners, including a group of young men wearing blue T-shirts reading: "I am a Muslim. Ask me anything?"
A woman who gave her first name as Jemana, from a mosque in Northolt, north London, was among a group of colourfully-dressed Muslim men and women carrying flowers.
"We've decided to come from our mosque as a community, to say that none of this that has happened resonates with what we understand as Islam, and that we are very sorry for what has happened," she said.
"We're together, we're all Londoners, we're all British."
Seven people were killed on Saturday when three men aboard a white van mowed down pedestrians on London Bridge before slashing and stabbing people at nearby Borough Market, a warren of bars and restaurants.
Forty-eight people were injured, 18 of whom remained in a critical condition on Monday.
In a brief speech at the vigil, London Mayor Sadiq Khan seemed to speak for many as he voiced his sorrow and anger.
"London stands in defiance," said Khan.
To applause and cheers, Khan described himself as "a proud and patriotic British Muslim" and coldly slapped down those who invoked Islam to justify acts of murder.
"You do not commit these disgusting acts in my name," he said. "To the sick and evil extremists who commit these hideous crimes, we will defeat you. You will not win."
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Less than half a mile (one kilometre) away, people stopped to look at dozens of bunches of flowers left at the southern end of London Bridge, which was cordoned off by police vehicles.
"Like a phoenix London will rise more beautiful and stronger. Hate will not win. Forever in our memories," read a note written on Metropolitan Police Service memo paper, attached to a bouquet.
Another, written by the "Boro Bistro family," said in French: "Alex, I hope that the place where you are now will be even more beautiful and peaceful than the desert of Jordan. With all my love. Rest in peace."
A Frenchman killed in the attack worked at the bistro in Borough Market, French media reported.
Georgina Lewis, 33, was accompanied by her two-year-old girl as she laid flowers.
"It's a way to say how sorry I am for the people that died, and also to make a promise to do whatever I can for my daughter so that these kind of things don't happen again," she said, tears flowing, as she looked at her child.
Saturday's attack, claimed by the Islamic State group, followed a similar car-and-knife assault by a lone attacker on Westminster Bridge on March 22 that killed five people and injured more than 50.
In the northwestern English city of Manchester, 22 people died in a suicide bombing on May 22, and 116 were injured.
