Last week, Bostonians gathered on their Commons for the annual lighting of the city's Christmas tree.
Not unusual, that -- it happens in cities and towns everywhere. But this tree is special. It didn't come from Massachusetts, or anywhere else in New England.
Instead, it came from a foreign country, an annual "thank you" to the city and people of Boston for their help during a catastrophe 100 years ago today.
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On Dec. 6, 1917, the world was at war. Halifax harbour was then, as it is now, a major port of departure for shipping.
Just before 9 a.m. that day, however, two vessels collided in the narrow channel between the ocean and harbour. They weren't going particularly fast, and the damage appeared minimal.
But a fire broke out on one: the SS Mount-Blanc. It drifted to shore, abandoned by its crew, while sending a column of smoke skyward, which attracted the fascinated attention of those who could see the plume.
Then it detonated.
For the Mount-Blanc was a heavily laden munitions ship, and that explosion was the biggest man-made blast ever until Hiroshima.
At least 2,000 people were killed outright, more were blinded by flying glass from the windows they'd been peering out of. The city's north end was levelled or rendered uninhabitable, and the final body wasn't recovered from the rubble until 1919.
The news was quickly flashed, not least by a lone railway dispatcher who stayed at his post when he realised what was about to happen. An oncoming passenger train was advised to halt, which it did, and hundreds more lives were saved.
But not Patrick Vincent Coleman, who died at his telegraph key, still sending out his final warning: "Hold up the train. Ammunition ship afire in harbor making for Pier 6 and will explode. Guess this will be my last message. Good-bye boys."
Canadians quickly rallied to the devastation, but a blizzard of epic proportions east of Nova Scota prevented relief from getting through from that direction.
Boston, however, was outside the range of the blizzard, and by the next day, doctors, nurses, medical supplies, bedding, clothing, food and other necessities were on their way to the beleaguered port.
That timely -- and unexpected -- intervention saved many more people from a slow death from injury, starvation or exposure. Lessons learned about treating eye injuries in particular are still enshrined in medical textbooks.
So every year, Nova Scotians scour the province for the likliest tree (this year's came from Cape Breton Island), carefully fold up its branches, cut it down and ship it south.
Halifax will never forget.