While I agree that all of our cities must be connected by rail, ASAP, we do need to prioritize which cities need to be connected first. Should an AI civ attack us, their force will consist mostly of cavalry, which are very mobile. They could literally wreck havoc through our interior if we cannot catch them, using rails. Where they to attack the SE of Thebes, we could simply fortify our units in the cities and let them run around without any great loss. However, if they attack in the other areas of our empire, they would be able to strike at many cities at once, and so we would need to get to them and destroy them almost immediately. Otherwise they would tear up improvements, kill workers, and possibly take a city or two because we had to spread our defenses very thin to defend all cities they could strike at. For these reasons, I believe a railway connecting our major cities in the "Old" empire to the Forbidden Palace in Thebes in vitally important.