I got the idea whilst looking at a map (something I tend to do often, considering this is an alternate history website) that perhaps the site of Lisbon or the strait of Gibraltar could provide a good possible site for a city that will be able to funnel trade from the Atlantic, as well as have good ground for a new city. Not very plausible, but I thought it may be interesting to have the eastern capital as Constantinople, middle as Rome, and western as Hispania or something. Any ideas for how this could occur?