There is a famous epic which claims that some of the concrete skyscrapers of Castelia City predate human occupation of the site. According to this tale, Castelia was originally a Conkeldurr city, which was stolen by humans in a war started because Unova had become so overpopulated that people had come to covet these pokemon's homes. The war was long and brutal, and although ultimately won by humanity, it was only through extensive use of powerful flying pokemon such as Braviary. Yet when the survivors surrendered, the conquerors became overcome with guilt, and allowed the Conkeldurr to continue living in the city, provided they allowed humans to move in as well; a compromise made possible by the extensive deaths on both sides which left the surviving populations small enough to share the city with ease.
There is truth in this legend, but many details have been distorted by time and the embellishments of storytellers. The story can not be securely placed in Castelia, and many scholars proposed alternative locations for the site of the war. The Conkeldurr city as it is usually depicted did not look like modern Castelia, except that it was made of concrete; the towering structures of the modern city are all of human design. This is because Conkeldurr are flightless creatures, and lacked the engineering advances which allow for modern skyscrapers to become convenient; to them, a 47-story building would have been more like a prison than a home. And the Conkeldurr population was not a group of wild pokemon which evolved urbanization in parallel with man; they had spent much of their lives building human settlements, and ran away when faced with new owners who mistreated them.
The claim that Conkeldurr building techniques such as concrete pillars were adopted by humans, however, is absolutely true.