On December 6, 1917, a French cargo ship exploded in Halifax Harbour, killing nearly 2,000 and levelling 1,600 homes. Within hours, the City of Boston dispatched a relief train carrying food, water and medical supplies to help the survivors. The next year, Halifax sent Boston a Christmas tree in thanks — a tradition that was revived in 1971, and continues to this day.

Earlier today, the 42nd annual Tree For Boston — a 15-metre white spruce — left its home on the property of Mary Lou Milligan of Mill Cove, Nova Scotia, headed for Beantown, where it will become the city’s official Christmas tree. Before that, it will pass through Halifax for a ceremonial stop at the city's Grand Parade square. The tree is scheduled to arrive at Boston Common on Friday, and will be unveiled in an official, televised tree-lighting ceremony December 5.

Via Cape Breton Post

Correction: An earlier version of this article implied that the Norwegian vessel SS Imo exploded in 1917. In fact it was the French cargo ship SS Mont-Blanc. For more on the Halifax Explosion, see this CBC website.