This and other laws defined slaves as their master's property at the same level as cattle. It also described a procedure for giving a slave their freedom. A freed slave did not have full legal status; for example, the punishment for killing a former slave was low. A former slave's son also had a low status, but higher than that of his parents. The Norwegian law code from 1274, "Landslov" (Land's law), does not mention slaves, but former slaves. Thus it seems like slavery was abolished in Norway by this time. In Sweden, slavery was abolished in 1343. British Wales and Gaelic Ireland and Scotland were among the last areas of Christian Europe to give up their institution of slavery. Under Gaelic custom, prisoners of war were routinely taken as slaves. During the period that slavery was disappearing across most of western Europe, it was reaching its height in the British Isles: the Viking invasions and the subsequent warring between Scandinavians and the natives, the number of captives taken as slaves drastically increased. The Irish church was vehemently opposed to slavery and blamed the 1169 Norman invasion on divine punishment for the practice, along with local acceptance of polygyny and divorce. In considering how serfdom evolved from slavery, historians who study the divide between slavery and serfdom encounter several issues of historiography and methodology. Some historians believe that slavery transitioned into serfdom (a view that has only been around for the last 200 years), though there is disagreement among them regarding how rapid this transition was. Pierre Bonnassie, a medieval historian, thought that the chattel slavery of the ancient world ceased to exist in the Europe of the 10th century and was followed by feudal serfdom. Jean-Pierre Devroey thinks that the shift from slavery to serfdom was gradual as well in some parts of the continent. Other areas, though, did not have what he calls "western-style serfdom" after the end of slavery, such as the rural areas of the Byzantine Empire, Iceland, and Scandinavia. Complicating this issue is that regions in Europe often had both serfs and slaves simultaneously. In northwestern Europe, a transition from slavery to serfdom happened by the 12th century. The Catholic Church promoted the transformation by giving the example. Enslavement of fellow Catholics was prohibited in 992 and manumission was declared to be a pious act. However it remained legal to enslave people of other religions and dogmas. Generally speaking, regarding how slaves differed from serfs, the underpinnings of slavery and serfdom are debated as well.