The City of Void, as commanded by Prince Mureya to be built by the crew of the Void Fleet, had no city walls. In Mureya's view, such walls, only capable of repelling ground forces, served little purpose.
After all, in Mureya's perception, nearly all those he considered enemies had the ability to fly. Therefore, the wall's defenses relied more on the defensive power of the magic arrays rather than physical fortifications. These arrays could be set up using any building in the city as nodes.
In Mureya's plan, the City of Void was without walls. Their existence would hinder the city's expansion rather than being beneficial to it.
The defense of the City of Void consisted of cannon towers standing tall on the magical array nodes left by Mureya's design. Atop these enormous cannons, tens of meters high, in addition to one magical cannon, there were two giant magic-guided crossbows. These were designed specifically to shoot down large creatures flying in the sky.