Try the D20 "Last Days of Constantinople,"
Typing in "d20 Historical" into Google returns a lot of results. There's a lot of stuff out there for the d20 game if you look, both supplement and adventure.
You might want to convert ideas and situations from Viking-era or Biblical-era d20 stuff. There's the d20 Past supplement from WotC. I would think the Greek era stuff would be something you'd be interested in.
The Google search returns some threads on this forum about historical gaming that might be helpful. Try that, then narrow your search to "d20 Rome", "d20 Ancient Persia", and stuff like that.
HERE'S a link to Noble Knight's d20 Historical page. Don't forget homebrew campaigns, either. Something like CrusaderEarth might prove to be very helpful.
Also check Amazon. Their lists can be helpful, especially in finding third-part, non-WotC stuff like OGL Ancients.