So I was playing as the Byzantines and I thought that the excellent scholarii that come from Scholae Barracks aren't historically accurate for after 1204, but I wouldn't like to play without them. Then I thought, in late campaign, I already have a lot of provinces, entire Greece and Minor Asia, if this had happened IRL wouldn't the emperors reestablish the scholae barracks or some kind of professional order?

So let's suppose that there is the "knowledge" or "technology" to have the scholae barracks, and let's suppose that this technology is lost after 1204. Then we need to find a way to rediscover it. What about having some tech buildings that reflect the level a state has advanced? Buildings that are required to unlock high-tier units/buildings and they are only required to be built once.

For instance, suppose we have a building named "engineers' school". As long as this building exists somewhere within the state, every city can build highways (considering that they have built paved roads already).
When the city with tech buildings is conquered then the tech buildings disappear unless the faction that conquered it already has them, or has their equivalent (say, scholae barracks equivalent would be tier 1 or 2 miltary academy that the western Europeans have?)

What do you guys think?