When did Oslo become capital of Norway?

Oslo, or Opslo, was the ancient name of the capital of Norway. According to Norwegian tradition, the city was founded in 1048 by King Harald Haardraade. By the end of the fourteenth century it had become the chief city of the kingdom. In 1624 Oslo was destroyed by fire. King Christian IV immediately rebuilt the city on the opposite side of the Aker River and named it Kristiania, or Christiania as it is spelled in English. Oslo, however, continued to be the name of a suburb on the east side of the Aker where the original city had stood. After the First World War a popular movement began in Norway to have the name of the capital changed back to its ancient form. This was done July 11, 1924, by act of the Norwegian legislature. The law provided that after January i, 1925, Oslo would be the official name of the capital.