A further division in Anglo-Saxon society was between slave and free. Slavery was not as common as in other societies, but appears to have been present throughout the period. Both the freemen and slaves were hierarchically structured, with several classes of freemen and many types of slaves. These varied at different times and in different areas, but the most prominent ranks within free society were the king, the nobleman or thegn, and the ordinary freeman or ceorl. They were differentiated primarily by the value of their weregild or 'man price', which was not only the amount payable in compensation for homicide, but was also used as the basis for other legal formulations such as the value of the oath that they could swear in a court of law. Slaves had no weregild, as offences against them were taken to be offences against their owners, but the earliest laws set out a detailed scale of penalties depending both on the type of slave and the rank of owner. Some slaves may have been members of the native British population conquered by the Anglo-Saxons when they arrived from the continent; others may have been captured in wars between the early kingdoms, or have sold themselves for food in times of famine. However, slavery was not always permanent, and slaves who had gained their freedom would become part of an underclass of freedmen below the rank of ceorl.