Space cities trace their roots to the primitive 20th century space stations of MIR and Skylab. Building on the knowledge gleaned in the first centuries of space exploration, in the 23rd century, scientists used the newly created Plastasteel to create lighter, stronger, and more powerful space stations. Not only did these dramatically lower launch costs, but they also enabled scientists to create permanent vast metropolises in space. Lastly, the Space Engineer, a masterpiece of robotic engineering allowed for the construction of the first space cities.