The Swedish slave trade mainly occurred in the early history of Sweden when the trade of thralls (Old Norse: þræll) was one of the pillars of the Norse economy. During the raids, the Vikings often captured and enslaved militarily weaker peoples they encountered, but took the most slaves in raids of the British Isles, and Slavs in Eastern Europe. This practice lasted from the 6th through 11th centuries until formally abolished in 1335. A smaller trade of African slaves happened during the 17th and 18th centuries, around the time Swedish overseas colonies were established in North America (1638) and in Africa (1650). It remained legal until 1813. The slaves from Western Europe were mainly Franks, Anglo-Saxons, and Celts. Many Irish slaves were used in expeditions for the colonization of Iceland. The Norse also took Baltic, Slavic and Latin slaves. The Vikings kept some slaves as servants and sold most captives in the Byzantine or Islamic markets. Vikings navigated the "Highway of the Slaves" through the Aegean Sea and into Black Sea ports first established by Archaic Greeks, shoreline crossroads for human trafficking. The slave trade was one of the pillars of the Norse economy during the 6th through 11th centuries. The Persian traveler Ibn Rustah described how Swedish Vikings, the Varangians or Rus, terrorized and enslaved the Slavs taken in their raids along the Volga River. Thralldom was outlawed in 1335 by Magnus IV of Sweden for thralls "born by Christian parents" in Västergötland and Värend, being the last parts where it had remained legal. This however, was only applicable within the borders of Sweden, which opened up for later slave trade in the colonies. In the 17th century, Swedish slave traders started to become involved with the Atlantic slave trade. Between 1784 and 1878, Sweden maintained possession of a handful of colonies in the Caribbean. The Swedish colony of Saint Barthélemy functioned as a duty-free port and became a major destination center for slave ships. Slaves were brought in tax free by foreign vessels and the Swedish Crown made a profit by collecting an export tax when slaves were shipped out. Sweden was also a major supplier of iron for chains used in the slave trade. In the early 19th century, Sweden signed treaties with the United Kingdom and France to abolish the slave trade. In 1847, slavery was abolished in all parts of Sweden, including her colonies, on