The disaster crushed the festive hopes of thousands of Canadians in Nova Scotia: on December 6, 1917, two ships, one carrying relief for Belgium, which had been devastated by fighting in the First World War, another carrying several tonnes of high explosives, collided in Halifax harbour, sparking a fire. What followed was one of the worst peacetime accidents in history. The ammunition boat exploded, sending a tidal wave through the town, killing 1,400 people and leaving tens of thousands to face an unbearably bleak Christmas without shelter, in blizzard conditions. But a quick response to the disaster from the US town of Boston, Massachusetts led to a century-old tradition: the annual gift of a Christmas tree from Nova Scotia to the people of Boston. This tradition was documented in a viral twitter thread by the Canadian armed forces. After the explosion, US assistance arrived swiftly, with the governor of Boston sending a train laden with supplies even before receiving a request from Halifax. At sea, US naval ship <em>Tacoma </em>steamed towards the town, having heard the blast 83 kilometres away. Before long, residents of Boston and several US states were raising funds for the people of Halifax. The years of collaborative reconstruction work that followed would create lifelong bonds and started a tradition to commemorate America's help for Canadian citizens, in a time of unbearable tragedy.<br/> For Boston Parks and Recreation Department, the tradition this year was a sign of resilience despite Covid-19 restrictions. To Marty Walsh, the mayor of Boston, the gesture has stood the test of time as a symbol of how people can come together during a crisis: “This year’s celebration reminds us of the importance of working together when we face difficult challenges. As Boston helped Nova Scotia in 1917, the city and our residents must partner to keep each other safe and healthy from the Covid-19 pandemic," he told news agency CBS Boston.