In stoic London, the sirens are just part of the big city soundtrack.
But the gunshots were startling.
In a country where 500 counterterrorism investigations are underway at any one time, the sight of masked men with guns was frightening — all the more so at the foot of Big Ben.
And so mid-afternoon Wednesday, London had to take just a moment to compose itself.
"This is a day that we had planned for, that we all hoped would never happen. But sadly it is now a reality," said Mark Rowley, the Metropolitan Police's head of counterterrorism.
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In the indifferent rush of a London workday, a man armed only with a car and a knife was bound to slip through, killing three people before police shot him dead.
Painful, surely, for the security services, because London hasn't seen an attack of this scale since 2005. And in less than four years, police have managed to foil 13 Paris-style attacks — a fact they just shared with the public earlier this month.
Police have so many examples, they've started making podcasts for the public about how they brought down real-life plots.
But just as surely as a lone attacker would eventually evade London's security services and 24-hour surveillance, London was bound to recover quickly when it did happen.
Once the initial horror was over, the resilience that comes with living for years with a severe threat of attack resurfaced. Severe means an attack is "highly likely."
Once out of lockdown, people with backpacks and bikes left quietly. Black cabs arrived to pick up customers. Construction workers in yellow vests within view of Big Ben started up again.
Courteous civil servants politely refused interviews because, one took the time to explain, civil servants aren't supposed to talk to the press.
Others were happy to discuss the inevitability of it all.
"It was expected at some stage that something like this would happen in the U.K.," said a woman who had been under lockdown in a building near Westminster.
"We were just lucky it hasn't happened before now."
Democracy 'under threat'
Police, too, knew it was coming. Just four days ago, they staged the latest in a never-ending rotation of police exercises that simulate attacks. In this one, it was a hijacked tourist boat. Just a chance to demonstrate competence to deal with such attacks, God forbid one should happen, said a police spokesperson.
But it did happen. In Wednesday's very real scenario, the attack happened at the entrance to the world's oldest Parliament.
And there — just as it was on Parliament Hill in Ottawa in 2014— the attack was met with defiance.
"Parliament buildings all over the democratic world are under threat from those who want to destroy democracy and freedom. They won't succeed," said Conservative MP Martin Vickers, who was inside Parliament when the attacker struck.
Labour MP Chris Bryant, who had been under lockdown for hours without information, came out insisting that Parliament sit as usual today.
Hours earlier, Parliament's Twitter account had said it would, and Prime Minister Theresa May later confirmed as much.
Near Westminster, we're reminded that a few blocks away, plaques commemorate the lives of civilians killed in bombings during the Northern Ireland conflict.
"I have always worked in this area, so I was here when the IRA bombed it so — you kind of get used to it," said Michael Burrell. "It's just terribly sad."
London's mayor, Sadiq Khan, said "Londoners will never be cowed by terrorism."
There will be more armed and unarmed police on the streets, at tube stations, around Westminster. There will be tension over the Islamist connection to the attacks.
But yesterday, even with the backdrop of tragedy, London's usual, brash soundtrack played on.
Just a short distance away from the bridge where people had lost their lives, pub patrons sipped on lager, taking stock of the day. A woman snapped a photo of a display at a clothing store.
Thousands of Westminster workers were starting their way home on foot, busy talking on phones.
The phrase heard most often: "I love you."