How do I let every faction build highways?

[Olaf The Great]

I dont quite know what you're talking about then ... highways ??? do u mean roads such as the Persian Royal Road or Silk Route ... those exist only in places where they historically did. If you're talking about 'Roman Highways' ... then i dont think there are such things in the game. I might be wrong.

Prince

Romans get one extra form of Paved road thats even better ie-Highways.