Actually, mentioning Pythium: what made Byzantium - who they were based on - great was an ingenious soldier settling system of "themes" (defense districts with their own command structures, soldiers were given land out in the boonies so they would have a stake in defending them) and an awesome bureaucracy. I don't know how this could be modeled in game, however, except for maybe slightly better administration (income, supplies, resources) for the bureaucracy, and a bonus to PD (for the "theme" system).
Sorry, my Norse mythology is stale as old bread, but I know a lot about the Classical period.
