intensive carving period, with carvings of agriculture, warfare, ships, domesticated animals, etc. Petroglyphs with themes have also been found in Bohuslän, dating from 800 to 500 BC. Viking Period and Middle Ages: 800–1500 For centuries, the Swedes were merchant seamen well known for their far-reaching trade. During the 11th and 12th centuries, Sweden gradually became a unified Christian kingdom that later included Finland. Until 1060, the kings of Uppsala ruled most of modern Sweden except for the southern and western coastal regions, which remained under Danish rule until the 17th century. After a century of civil wars, a new royal family emerged, which strengthened the power of the crown at the expense of the nobility, while giving the nobles privileges such as exemption from taxation in exchange for military service. Sweden never had a fully developed feudal system, and its peasants were never reduced to serfdom. The Vikings from Sweden partly took part in the raids of the Western and Southern regions of Europe, but mainly traveled east to Russia, Constantinople and the Muslim world (Serkland). The large Russian mainland and its many navigable rivers offered good prospects for merchandise and plundering. During the 9th century, extensive Scandinavian settlements began on the east side of the Baltic Sea. The conversion from Norse paganism to Christianity was a complex, gradual, and at times violent (see Temple at Uppsala) process. The main early source of religious influence was England, due to interactions between Scandinavians and Saxons in the Danelaw, and with Irish missionary monks. German influence was less obvious in the beginning, despite an early missionary attempt by Ansgar, but gradually emerged as the dominant religious force in the area, especially after the Norman conquest of England. Despite the close relations between Swedish and Russian aristocracy (see also Rus'), there is no direct evidence of Orthodox influence. Around the year 1000, Olof Skötkonung became the first known king to rule both Svealand and Götaland. Historical details about early medieval kings are obscure, and even the dates of their reigning periods remain unclear. In the 12th century, Sweden was still undergoing dynastic struggles between the Erik and Sverker clans. Svealand and the Swedes were usually more supportive of the Erik dynasty and Götaland and Geats more supportive of the Sverker dynasty, which wanted friendlier relations with Denmark. This further divided the country between parties because the ruler was not clear. The country elected