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In early 1925, an outbreak of diphtheria threatened to wipe out the entire population of Nome, a remote gold rush town in Alaska. With no antitoxin at hand, an idea was proposed to have the much-needed medicine delivered by dogsled across some of the most inhospitable wilderness in the United States. What happened next remains one of the most heroic and inspiring episodes in US history.

So, was the serum successfully handed over? Click through this gallery and learn more about what became known as the Great Race of Mercy.

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Alaska Natives known as the Inupiat called their Nome Sitnasuak. The Inupiat are members of the Inuit culture, which spans the northern coasts of Alaska and Canada, and as far as Greenland. The west coast of Alaska has been their hunting ground for millennia.

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Nome in the 19th century was little more than a barren ribbon of sand where the Inupiat camped. Then in the summer of 1898, dozens more tents sprang up after prospectors discovered gold along a creek.

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By 1899, Nome Beach was awash with thousands of pioneers and frontiersmen housed under canvas hoping to strike it rich. A tent city reached reached 30 miles (48 km) from Cape Rodney to Cape Nome.

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In just seven years, houses had replaced tents. Nome had become a thriving community of stores, schools, saloons, a church, hospital, and post office. It even had an electric light plant.

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Nome soon grew into the biggest town in Alaska, with a population of 10,000. Steamships from the ports of Seattle and San Francisco brought thousands more.

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The Nome Gold Rush reached its height in 1905, when more gold was found in old beaches above the high-tide mark.

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It wasn't long before big business moved into the newly organized Nome mining district. The town's population doubled. Some prospectors made millions, their lucky strikes forged into glittering mountains of gold bullion.

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By 1909, the gold rush was over. Nome's population dropped to less than 3,000 and the town returned to a modicum of normality. By the early 1920s, just 1,420 people—settlers of European descent and Inupiat—remained.

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Nome lies approximately two degrees south of the Arctic Circle. In those days from November to July, the port on the southern shore of the Seward Peninsula of the Bering Sea was icebound and inaccessible by steamship.

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The only link to the rest of the world during the winter was the Seward-to-Nome Trail, which ran 938 miles (1,510 km) from the port of Seward in the south across the vast and unforgiving Alaska interior to Nome. The route is actually better known as the Iditarod Trail.

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In December 1924, Curtis Welch, the only doctor in Nome, expressed concern after several children complained of sore throats and swollen glands. He treated his young patients for what he first diagnosed as tonsillitis. But after the number of cases grew and four children died, Welch officially diagnosed diphtheria, a highly infectious disease.

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By January 1925, Welch realized that an epidemic was imminent and informed the local council. Nome's mayor immediately implemented a quarantine.

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By the end of January and despite the lockdown, over 20 more cases of diphtheria had been confirmed, many involving Inupiat children. To his horror, Welch discovered the hospital's entire batch of diphtheria antitoxin had expired. Without it, those in Nome and the surrounding region's population would be at serious risk of death.

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Anchorage, nearly 1,000 miles (1,609 km) away from Nome, had fresh supplies of antitoxin. Flying it in, however, was out of the question due to extreme weather conditions.

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Instead, Alaska's territorial governor, Scott C. Bone, proposed using teams of dogsleds to deliver the vital serum. This life-saving relay would become known as the Great Race of Mercy.

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Dogsledding was a traditional mode of winter travel in the area. But what the governor had in mind would test the stamina and resolve of the fittest dogs and most experienced of mushers. This map shows the serum run route marked in green, set across a portion of the Iditarod Trail.

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Twenty dogsled mushers and more than 150 dogs were selected to deliver the desperately needed medicine. Among these was the Norwegian sled dog trainer Leonhard Seppala. Leading his team of dogs was Togo.

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Gunnar Kaasen, one of Seppala's assistants, was also added to the relay. His lead dog was Balto. Contrary to popular belief, neither dog was a Siberian Husky. Instead, both shared ancestry with modern Tibetan Mastiffs, sled dogs from Greenland, and dogs from Vietnam, well suited to Alaska's harsh climate.

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On January 27, 1925, 30,000 units of antitoxin was shipped by rail to Nenana, the relay's starting point. While not sufficient to defeat the epidemic, this was enough to slow the spread of the disease until a larger shipment arrived.

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The first teams of mushers and dogs departed Nenana to meet high winds and frigid temperatures as low −85°F (−65°C) before handing off to the next team. Heavy snow further hampered the progress of all involved.

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Meanwhile on the same day, January 27, Seppala and his dog sled team set off from Nome. Seppala would eventually rendezvous with Henry Ivanhoff's westbound team outside Shaktoolik to receive the serum. Conditions remained treacherous, and hypothermia and frostbite were ever-present risks.

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Seppala turned around with the serum and reached Ungalik after dark. After resting in one of the many roadhouses set along the route, he braved the exposed open ice of the Norton Sound and passed the serum to Charlie Olsen on February 1.

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Olson, suffering severe frostbite, met with Gunnar Kaasen at Bluff later that night. Kaasen backtracked and continued through the dark in stinging snow, pressing on with the remaining 25 miles (40 km) to Nome. He arrived in the town at 5:30 on the morning of February 2, 1925. This photo shows the triumphant arrival of Kaasen's dog team.

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Not a single ampule was broken during the 674 miles (1,085 km) the relay teams covered in the five and a half days it took to reach Nome from Nenana.

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This was mainly due to the fact that the 300,000 units had been encased in a 20-pound (9.5-kilo) cylinder and wrapped in fur to prevent freezing. Pictured is the cylinder's envelope, addressed to Dr. Welch.

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The Great Race of Mercy caught the imagination of the nation. Both the mushers and their dogs were portrayed as heroes in the newly popular medium of radio and received headline coverage in newspapers across the United States.

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Balto, the lead sled dog on the final stretch into Nome, became the most famous canine celebrity of the era after Rin Tin Tin. His hero status afforded the canine a permanent memorial when sculptor Frederick Roth created a statue of the famous four-legged savior.

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Dedicated on December 17, 1925, the bronze statue is on display in Central Park in New York City. Balto himself passed away in 1933.

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The dog was further immortalized in the 1995 animated adventure film 'Balto.' Actor Kevin Bacon voiced the titular canine. Bob Hoskins, Bridget Fonda (pictured with Eric Stoltz), and musician Phil Collins also lent their vocal skills. The film spawned two sequels, 'Balto II: Wolf Quest' (2002) and 'Balto III: Wings of Change' (2005).

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Further projects have been made based on the events that took place in Alaska in 1925. 'The Great Alaskan Race' stars Brian Presley as Leonhard Seppala and Treat Williams as Dr. Welch.

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'Togo' centers on Leonhard Seppala and his titular sled dog. The film stars Willem Dafoe and Julianne Nicholson.

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Meanwhile, the annual Iditarod Trail Sled Dog Race travels from Anchorage to Nome, and at 938 miles (1,510 km) is the longest race of its kind in the world. Teams often race through blizzards, sub-zero temperatures, and gale-force winds, much like the conditions experienced by those involved in the Great Race of Mercy 100 years ago.

Sources: (Alaska State Archives) (Britannica)