As SpaceX's CEO Elon Musk has acknowledged, eventually Super Heavy booster stages for Starships could be manufactured on Mars as a launch platform for outer Solar system missions. Here is a vision of several Starship Super Heavy (in its 2016 design, then called Interplanetary Transport System) launch pads at Mars City's spaceport by US designer Casey Alexander.
"Mars City" is the name Elon Musk gave to SpaceX's future human colony on Mars (now referred to as "Mars Base Alpha") in some earlier presentations of SpaceX's Mars colonization architecture.