The officials faced a difficult decision. A suspected terrorist believed to be linked to a series of bombings days before had popped onto law enforcement's radar near public transportation and on the run.
At a hurried meeting to address the situation, the transportation secretary told the group, "This is an all or nothing proposition." Either they kept the whole city running or they shut it down.
The officials shut it down.
That was April 2013 in Boston, when law enforcement lost track of Dzhokhar Tsarnaev, one of the suspected marathon bombers, and ordered residents to "shelter in place," putting a large swath of the metro area on lockdown.
This weekend, Brussels made the same decision. The discovery of an active terror cell in the city with links to this month's Paris attacks led to the closure of public transportation, the cancellation of events, and a warning not to gather in crowds Saturday and Sunday. With the suspects still at large, the shutdown is expected to continue Monday.
The decisions in both Boston and Brussels came from a known threat, with events unfolding rapidly. But more deeply, they also point to something approaching an atmosphere of war footing in the West.
The French president has declared the Paris attacks an act of war, and Republican governors in the United States have vowed to block any efforts to bring Syrian refugees to the country.
In time, these might prove brief flashes. President Obama, addressing the refugee situation, has said: "My expectation is, after the initial spasm of rhetoric, that people will settle down."
But there are also signs that the Islamic State, which has claimed responsibility for the Paris attacks, has unsettled the West more deeply through the abhorrence of its actions.
One poll last year suggested that Americans felt significantly less safe than at any time since 9/11. A new poll finds that 83 percent of Americans think a terrorist attack with mass casualties is likely soon.
The results are renewed attempts by politicians and public officials to draw some semblance of a front line in a war that has none. This weekend, Belgian officials drew the line at residents' front doorsteps, keeping civilians at home to deny a suspect described as possibly "ready to blow himself up" any potential targets.
But in American states and in France, efforts to draw that line farther from the homefront – at the American border or on the Islamic State's own doorstep – only underscore the difficulty of the path ahead. Evidence suggests neither ramping up air strikes against the Islamic State nor keeping out Syrian refugees would effectively rein in terrorism.
The question posed by Brussels – like Boston before it – is how countries will react when terrorism does come home.
For their part, Boston officials have said that their shutdown – which lasted less than one day – worked. Mr. Tsarnaev was found and captured shortly after the shutdown lifted. "The bottom line was we got a very good search done that basically flushed him out of a certain area,” said Boston Police Commissioner Ed Davis in an interview with WGBH radio that included the account of the emergency shutdown meeting.
But others have questioned the decision. They call it a sign of the "ratchet effect" – government steadily expanding its influence in times of crisis. "When the crisis abates, government power does, too, but never completely back to where it was before. With each subsequent crisis, government encroaches a bit more," writes Radley Balko, a criminal justice blogger for The Washington Post. "The effect may be particularly pronounced and dangerous with respect to the war on terror, because as crises go, terrorism can never completely be defeated."
French Defense Minister Jean-Yves Le Drian has vowed that the Islamic State can be defeated. "We must annihilate Islamic State worldwide ... and we must destroy Islamic State on its own territory," he said.
At this point, there is little evidence to suggest that can be done through air strikes. As Ishan Tharoor of The Washington Post notes: "The closest the United States has come to destroying a terrorist organization like the Islamic State was when it subdued the al-Qaeda insurgency" in Iraq. That required about 170,000 American troops, and after the troop surge abated, Iraq's Al Qaeda branch mutated into today's Islamic State.
Prescriptions to keep Syrian refugees out of the United States appear similarly reactive. Despite reports that one of the Paris attackers posed as a refugee, terrorists are unlikely to use the same route to get into America, given that refugees can't set foot in America until they have had up to two years of vetting, The Atlantic explains. Other ways into the US are simpler.
In Belgium, officials say they are doing their best to cope with a dynamic and dangerous situation. "We are following the situation minute by minute. There is no reason to hide that," Interior Minister Jan Jambon told reporters.
Lessons from the blitz
Before the German bombing blitz of World War II, British citizens were exhorted to keep calm and conspicuously carry on. Now, in a very different way, Brussels is bringing the same questions into focus for a new age of warfare: When do citizens carry on, and when do they hunker down?
During the blitz, the nighttime hours – when the threat was greatest – was a time for hunkering down in bomb shelters. But the nightly eight-month bombing campaign, which killed some 42,000 Britons, didn't break the British spirit because they were prepared for it, writes historian Richard Overy in The Guardian.
"The blitz was the kind of war the British public had expected and been prepared for. Millions of ordinary people worked in air raid precautions and the auxiliary services, undertook firewatching, or joined the home guard," he said. "Civilians were now in the frontline, and thousands wore uniforms and were trained, just like soldiers. The capacity to withstand bomb attack owed much to the process of 'militarising' civilians."
Today, the preparation for a war that can strike anywhere for no strategic purpose other than to terrorize is in many ways even more mental, suggested Mr. Obama while speaking in Asia Sunday.
"The most powerful tool we have is to say we are not afraid," he said.
On the streets of Paris, that deeper battle is already being fought.
"I don't think I will live differently," Parisian Valerio Geraci told NBC News. "I will just try to fight with my fear."