I push my magic into the tower and watch with delight when it begins to glow. I placed the towers around the entire City like a large circle. In theory, The power I push into the first tower will begin spreading to the other surrounding towers.
Once every tower is glowing, all I need to do is continue pushing the power in one direction. The coils, glass, and mirrors placed inside the towers will then act as conductors. Once the flow has been established I can remove my hand. In a way, it's like a gigantic lightbulb but with magic.
The flow of energy should continue flowing around and around as long as nothing happens to the towers. It'll act as a force field for the City. As I placed the towers in the ground I wrote a symbol of invisibility on them in order to protect them.