Merchant City: Mer Covales, the capital of Seranth (which is not, however, the throneworld), itself located at the junction of the Lethíäza Trade Spine and the Mercantile Corridor, the two biggest and oldest trade routes in the Associated Worlds.
Imagine, if you will, New York City, Hong Kong, and Singapore glommed together into one giant mass of wealth and commerce. Then scale up what you’re imagining until the buildings look like Coruscant’s giant arcology-towers, remake it out of the costliest materials you can imagine, divide it into three concentric layers stacked one above the other, make the whole thing fly, and dangle it off the end of an orbital elevator.
That’s Mer Covales, a giant, hovering testament to wonders, riches, mystery, risk, vice, luxury, splendor, and the ability of wealth to be as potent a force in reshaping the universe as any of the other four, if not more so. If you can’t buy it there, not only does it not exist, but there’s literally no-one you can pay to make it exist.