- the AI does not build them;
- not all civs have them;
- their stats are rather arbitrary;
- there appears to have been no proper discussion or extensive play-testing;
- the right selection panel can only display up to 24 entities.
This patch ensures ordinary towers can't be upgraded to artillery towers or bolt towers and that those can't be built directly.
They remain still available for maps and mods. The same applies to the stables etc added last year.