The race, which is held annually in February, was started in 1973 by Tony Wise. Wise, who started the Telemark Ski Area in Cable, Wisconsin in 1947, helped to popularize modern-day cross-country skiing when he built trails at Telemark in 1972. In February 1973, Wise drew on his Norwegian heritage in starting a race named after a famous event in Norway.
The Birkie was named after the Norwegian Birkebeinerrennet, which commemorates an important historical event. In 1206 a group of Birkebeiner party soldiers, who fought for Sverre Sigurdsson and his descendants in the Norwegian civil war, smuggled the illegitimate son of Norway's King Håkon Sverresson from Lillehammer to safety in Trondheim. In the Norwegian Birkie, skiers still carry packs symbolizing the weight of an 18-month-old child. The packs also contain extra food, clothing and survival gear to protect against unexpected weather changes in the harsh sub-Arctic mountains that the skiers cross during the race.
Skiers from around the world come to Hayward, Wisconsin for the race. The Birkie has a reputation for attracting skiers of varying ability levels. Olympians and national team members have competed in the event, and the Birkie also draws recreational skiers from Wisconsin, Minnesota, and the Upper Peninsula of Michigan and countries such as Canada. The race day also includes the shorter 23 km Kortelopet "Korte", a race geared more toward recreational skiers, and the Prince Haakon 13 km event for those who are not ready to take on the challenge of the longer courses. Registration is capped at 10,000 skiers in 2013, with an additional 20,000 spectators on the sidelines cheering on the competitors.
The Birkie course is quite hilly, and is recognized as one of the more difficult cross country ski marathon courses in the world, despite the fact that there are several World Loppet events in Europe that are much longer. The current north-south alignment (used since 1992) has skiers traversing a 2 km (1.2 mi) flat section before turning onto the "Powerline Hills", a series of climbs to the 4.5 km (2.8 mi) mark. The trail then rolls until 12 km (7.5 mi), when Firetower Hill takes competitors to 1,730 ft (530 m), the high point of the race and a climb of nearly 400 ft (120 m) from the race start. In early years of the race, the Birkie began with a climb up the alpine slopes of Mount Telemark, mainly as a publicity stunt, but larger field sizes made this impractical. Beyond High Point is a series of downhills, including "Bobblehead Hill" or "Sledder Hill", which has a rather tricky downhill, right turn near a snowmobile trail — allowing dozens of snowmobilers to watch and "score" skiers' falls. The trail rises steeply to the crossing of County Road OO (Referred to as "Double-Oh") which, at 22.8 km (14.2 mi), is the unofficial halfway point of the race. Until 2001, the 23 km (14 mi) Kortelopet race ended here but has since been rerouted back to Telemark after splitting off from the main course at 9 km (5.6 mi).
Beyond OO the course is less hilly, but by no means flat. After 40 km (25 mi) is the aptly named "Bitch Hill" where spectators cheer skiers up the steepest climb of the race. Several kilometers later (just south of Highway 77) is the last lengthy ascent of the race—El Moco—known for its numerous bends, each offering the empty promise of a summit. From the top, Hayward's watertower is a most welcome sight. There are several road crossings and open fields before the course crosses frozen Lake Hayward. The 4 km (2.5 mi) crossing of the lake is obviously flat, but unprotected from wind. Once off the lake the trail twists through the outskirts of Hayward on snow trucked in for the event. Over the course of hours thousands of tired and proud skiers make their way past three blocks of cheering spectators lining Hayward's Main Street. Warm conditions have occasionally required the finish line be moved to a flat field just west of the lake.
The race begins with several waves in order to thin skiers out along the course. Alternating skate and classical waves depart every five minutes. New skiers must ski in the last Wave unless they use another ski marathon time to qualify up. One man has completed every Birkie since the first one in 1973; Ernie St. Germaine, a former employee of the Telemark Resort, where the Birkebeiner starts every year.
According to wikipedia