In 1917, Bostonians reacted to an unprecedented tragedy in Halifax with an outpouring of support and resources. Nearly a century later, Nova Scotians haven’t forgotten.

On December 6, 1917, a French ship named the Mont-Blanc was passing through Halifax Harbor, making its way from New York to France. The ship was carrying a staggering load of munitions: 2300 tons of picric acid, 35 tons of benzene, and 200 tons of dynamite. If you think this sounds like an accident waiting to happen, you’re absolutely right. At 8:45 a.m., the Mont-Blanc collided with a Norwegian cargo ship called the Imo. At first, the French ship simply caught fire, inspiring thousands of people to gather into the harbor to watch.

Then, at 9:04 a.m., it exploded—and the impact was devastating. More than 1500 people were killed instantly; everything within a 1.2-mile radius was completely flattened and scorched. In addition to crushing schools, factories, and churches, the explosion destroyed more than 1600 homes and left 6000 people homeless. To this day, it remains the largest non-nuclear explosion in history.

WarBaCoN via WikimediaCommons // Public Domain

Boston's friendly relationship with Halifax dates back to the 1700s, when the cities formed a relationship over shipping and the fish trade. When word of the tragedy hit Bean Town, residents immediately sprang into action. More than $100,000 was reportedly raised in the first hour of relief efforts, and $30,000 worth of Army blankets were sent via car. A train brought 30 of Boston’s leading physicians and surgeons, 70 nurses, a 500-bed base hospital unit, and hospital supplies. The Boston Symphony performed a sold-out benefit concert to aid Halifax in the week following the disaster. By the time all was said and done, Massachusetts had contributed more than $750,000 to the relief effort.

To thank Bostonians for everything they had done, residents of Halifax sent them a large Christmas tree the following year. They repeated the gift in 1971 and have done it every year since. The trees, which eventually make their way to Boston Common, are sometimes donated by people who had relatives that died in the blast, and sometimes government officials identify the perfect tree and ask the owners to consider donating it. The trees must meet certain specifications, including height (40-50 feet), type (balsam fir or white or red spruce), and shape (uniform and symmetrical).

Louis Olivera via Wikimedia Commons // CC BY-SA 2.0

Nova Scotians used the 2013 tree delivery to return the city's thoughtfulness in the face of tragedy. Three marathon runners led the tree out of Halifax to honor the victims of the Boston Marathon bombings.