Oslo was formerly known as Christiania, later Kristiania, until the city officially reclaimed the name Oslo on 1 January 1925. The modern capital’s name therefore reaches back to the medieval settlement that existed before the early modern city was moved and rebuilt.
A major fire destroyed medieval Oslo in 1624. King Christian IV of Denmark–Norway ordered the town rebuilt closer to Akershus Fortress, and the new settlement was named Christiania after him. The spelling gradually changed to Kristiania in Norwegian usage during the nineteenth century, although Christiania remained familiar internationally.
The city became the capital of the independent Kingdom of Norway in 1814, after the country ended its long union with Denmark. In the early twentieth century, Norwegian cultural and political opinion increasingly favored restoring the older Norwegian name. Parliament approved the change in 1924, and it took effect the following year.
The name change can be confusing because “Oslo” also continued to refer to the older medieval area while the newer city used Christiania or Kristiania. In 1925, the municipality’s official name became Oslo, bringing the historical names together.