These unused Town Center architectures are located between the Bronze Age and Iron Age architecture.
Complete graphics for all four distinct building styles exist (there are none for Rome in the expansion though). It can be placed on a custom map with some hacking, but it has no function at all. The trade workshop is an unused building.
These four upgrade icons are not used in the game, and were likely used by some of the above units for researching them. A bunch of unused text exists for researching several units which in the final game you can train/build straight away:
It seems that a lot more units were required to be researched before you could train/build them.
