Dog sledding began in Canada and Alaska where people were dependent on their dogs for protection, companionship, hunting, trapping and, most of all, transportation. Sled dogs enabled explorers such as Byrd, Peary and Amundsen to explore the frozen wastelands of two continents. They have helped men in two World Wars and of course, the Canadian Mounted Police owes much of its fame to teams of sled dogs. One of the greatest moments in dog sled history was in 1925. In the depth of winter, diphtheria was discovered in Nome, Alaska and the supply of serum in the city was inadequate to stave off an epidemic. A relay of twenty-two teams forged through Alaska and across the Bering Sea ice to bring supplies from Anchorage. The Iditarod Trail Race has been held every year since to commemorate the Nome Serum Run.