A depiction of 9th century Vikings abducting a woman. Viking men

would often kidnap foreign women for marriage or as concubines.

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Concubinage was part of Viking society, whereby a woman could live with a man and have children with him without marrying; such a woman was called a Frilla. Usually she would be the mistress of a wealthy and powerful man who also had a wife. The wife had authority over the mistresses if they lived in her household. Through her relationship to a man of higher social standing, a concubine and her family could advance socially; although her position was less secure than that of a wife. There was no distinction made between children born inside or outside marriage: both had the right to inherit property from their parents, and there were no "legitimate" or "illegitimate" children. However, children born in wedlock had more inheritance rights than those born out of wedlock.

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Source: Wikipedia