Just came across this today - Soren Johnson and Dorian Newcomb discuss the development of Civ4, complete with examples of prototype builds as work on the game progressed. I had somehow missed this great video at the time it originally came out, so I figured I'd share it here in case anyone else also hasn't seen it yet. Well worth a watch for anyone interested in hearing more about how a game like Civ4 comes together.
Link to the playlist on Youtube
Link to the playlist on Youtube