Of course, even though this is a city of the Ghost Race, it doesn't necessarily mean that the city was entirely built by them. Because to support such a massive city, the group must possess strong productivity.
During the time of the Aud Empire in the Western Continent, the might of the Aud Empire was once powerful, and productivity soared tremendously. Now, a considerable number of city constructions in the northern part of the Western Continent are basically legacies from the era of the Aud Empire. On the contrary, after the Empire split, the productivity of each independent Kingdom declined significantly.
Baiyue was not sure whether these buildings were related to the Kyushu Empire's invasion, because from the current situation, the entire civilization of the East Continent had been more or less influenced by the civilization of the Kyushu Empire, just as the civilization of the Western Continent originated from the Aud Empire.