strength through wrestling (see glima), fist fighting, and stone lifting. In areas with mountains, mountain climbing was practised as a sport. Agility and balance were built and tested by running and jumping for sport, and there is mention of a sport that involved jumping from oar to oar on the outside of a ship's railing as it was being rowed. Swimming was a popular sport – Snorri Sturluson describes three types: diving, long-distance swimming, and a contest in which two swimmers try to dunk one another. Children often participated in some of the sport disciplines, and women have also been mentioned as swimmers, although it is unclear if they took part in competition. King Olaf Tryggvason was acclaimed for his skill in both mountain climbing and oar-jumping, and reputedly excelled in the art of knife juggling as well. Skiing and ice skating were the principal winter sports, and also provided transport on snow and ice for adults. Horse fighting was practised for sport, although the rules are unclear. It appears to have involved two stallions pitted against each other, within smell and sight of fenced-off mares. Whatever the rules were, the fights often resulted in the death of one of the stallions. Icelandic sources often mention knattleik, a ball game similar to hockey, played with a bat and a small hard ball, usually on a smooth surface of ice. Popular with both adults and children, it was a rugged game that often led to injuries. Knattleik appears to have been played only in Iceland, where it attracted many spectators, as did horse fighting. Hunting was practiced as a sport only in Denmark, where it was not an essential food source. Deer and hares were hunted for meat, along with partridges and sea birds, while foxes were hunted to stop their killing of farm animals and for their furs. Spears, bows, and later crossbows, were the weapons used; stalking was the most common method, although game was also chased with dogs. Numerous kinds of snares and traps were used as well. Games and entertainment Archaeological finds and written sources indicate that the Vikings participated in social gatherings and festivities. Board games and dice games were a popular pastime. Game boards were made of ornately carved wood, with gaming pieces fashioned mostly from wood, bone, or stone. Pieces were also made of glass, amber, and antler, along with materials such as walrus