the lowest ranking class and were slaves. Slaves comprised as much as a quarter of the population. Slavery was of vital importance to Viking society – for everyday chores and large scale construction and also to trade and the economy. Thralls were servants and workers on the farms and in larger households of the karls and jarls, and they were used for constructing fortifications, ramps, canals, mounds, roads and similar projects built by hard labor. According to the Rígsþula, thralls were despised and looked down upon. New thralls were supplied by either the sons and daughters of thralls, or were captured abroad by the Vikings on their raids in Europe. The thralls were brought back to Scandinavia by boat, used on location or in newer settlements to build needed structures, or sold, often to the Arabs in exchange for silver. Other names for thrall were træl and ty. Karls were free peasants. They owned farms, land and cattle and engaged in daily chores like ploughing the fields, milking the cows, building houses and wagons, but used thralls to make ends meet. Other names for karls were bonde or simply free men. Similar classes were churls and huskarls. The jarls were the aristocracy of Viking society. They were wealthy and owned large estates with huge longhouses, horses and many thralls. The thralls did most of the daily chores, while the jarls carried out administration, politics, hunting, and sports – they also visited other jarls or went abroad on expeditions. When a jarl died and was buried, his household thralls were sometimes sacrificially killed and buried next to him, as many excavations have revealed. In daily life, there were many intermediate positions in the overall social structure and it appears that there was some social mobility between them. These details are unclear, but titles and positions like hauldr, thegn, and landmand, show mobility between the karls and the jarls. Other social structures included the communities of félag in both the civil and the military spheres, to which its members (called félagi) were obliged. A félag could be centred around certain trades, a common ownership of a sea vessel or a military obligation under a specific leader. Members of the latter were referred to as drenge, one of the words for warrior. There were also official communities within towns and villages, the overall defence, religion, the legal system and the Things. Status of