C3621 Black Dragon Iron

Lu Yu didn't pay any attention to him. Instead, his gaze fell upon the stone bricks on the city wall.

"This is not the current era's craftsmanship. This is the forging method from the ancient times. There was a large amount of Black Dragon Iron in the Middle Ancient Era. When it was used to make the bricks on the city wall, these iron scraps would mix in. It would make the walls indestructible