The four cities were constructed by the Ru'Harem after the completion of Novaru and discovery of human life on Ru'un. It is not know how, why, or exactly when they were constructed but it is likely that the cities existed before human civilisation of any kind. The four cities consist of Akeroe (Ake'ro) the mountain city, Basurae (Basu're) the underwater city, Kakkorom (Kakk'rom) the volcano city of the North and Valrier (Val'rie) the "sky city" or "Swift City".
The four cities are commonly personified as a group of siblings. this is mainly due to the emytology of each city, based on the masculine and feminine derivatives of the Ru'an word Raa, meaning city. Akeroe is described as the eldest and strongest, with Basurae as the eldest sister representing healing. Kakkorom is often described as the angry and destructive younger brother while Valrier, being the youngest, is the little sister eager to learn. Ru'nian mythology has many stories with characters based on the four cities, with the dynamic of the four siblings and their relative attributes offering a stable character dynamic for storytelling.