Trade Metropolises are similar to Capitals, however instead of towering arches, it is a town centre with a Big Ben style clock. Instead of giving Kingsguard Units, it gives the entire alliance increased food production. This is regarded as extremely useful amongst higher level players due to the increased number of soldiers they can recruit.
Trade Metropolises are about as rare as Capitals are. However, the Official Announcement did say that there will be more TMs than Capitals, because its population requirement is much lower than that of a Capital.
Inside the Trade Metropolis
When you first capture a Trade Metropolis, or "Metro" as they are referred to, the castle view is instantly maximum size with level 3 walls, gates, towers, and keep. Instead of the Royal Storage, which is found in a Capital, you get a Merchant's Storage, and instead of a Palace, you get an Emporium.
The Emporium costs