Organized education in Norway dates as far back as medieval times. Shortly after Norway became an archdiocese in 1153, cathedral schools were constructed to educate priests in Trondheim, Oslo, Bergen and Hamar. After the reformation of Norway in 1537, (Norway entered a personal union with Denmark in 1536) the cathedral schools were turned into Latin schools, and it was made mandatory for all market towns to have such a school. In 1736 training in reading was made compulsory for all children, but was not effective until some years later. In 1827, Norway introduced the folkeskole, a primary school which became mandatory for 7 years in 1889 and 9 years in 1969. In the 1970s and 1980s, the folkeskole was abolished, and the grunnskole was introduced. Oslo, Norway, 2012.