Pylons were massive, energy-based weapons designed by Red Sun. Originally built to funnel
unusable energy away from Titan, they soon doubled as defensive weapons, able to badly damage nearby Allied units. Shutting a pylon down could be acomplished in two different ways: either capture the power plant fueling it, or smash the pylon itself.
Twelve pylons surrounded the heart of Project:Titan, and were destroyed in order to overload the weapon and destroy it.
Normally, cities cannot fuel a pylon, as they amount of power they require is enormous.