Because of the intensity of the clash between Nolan and Ruin's magic attacks, the two had subconsciously moved to a larger space.
After confronting each other for hours, the area around them had already been deformed. It was likely that any local who saw the surroundings would have trouble recognizing it. They might even think it was no longer part of the city. It was the proof of the power the two clashing mages had unleashed thus far.
Anyone who was aware of how long the two had been confronting each other would also believe they were already nearing their limit. However, neither showed any signs of exhaustion. As a matter of fact, both were as lively as ever.